Methanogens are the primitive bacteria belonging to archaea which are able to produce methane through the process of methanogenesis. These organisms can utilise the carbon dioxide and hydrogen gas to form methane. These organisms are found in marshy areas where they produce the marsh gas, in swamps and in the stomach of cattle. The methane is released along with the other wastes by the cattle and so, methane is found abundantly in the cattle yard. 

Monera is a kingdom that includes prokaryotic unicellular organisms. It includes bacteria, Eubacteria, Archaebacteria, Cyanobacteria. They lack membrane-bound organelles. They also lack true nucleus. Instead, they have nucleoid, genetic material without nuclear envelope.

Answer is option D i.e. "Both (A) and (C)"
Archarbacteria are salt loving bacteria that can live in strong salt solutions. Hence they are also called halophiles. In presence of strong sunlight they develop a purple colored pigmented membrane to utilize light energy producing ATP.

Enzymes synthesized by archaea (with optimal growth temperatures of >80 degree Celsius), also called hyperthermophilic enzymes, are typically thermostable ( that is resistant to irreversible inactivation at high temperatures) and are optically active at high temperatures. 

Thermophilic sulphur bacteria can survive at high temperatures between 41 and 122$^o$C and an optimum growth temperature which is higher than 75$^o$C. Hot spring blue-green algae have an optimum growth temperature of 45$^o$C. Methanogenic archaebacterium grows at an optimum temperature of 35-40$^o$C. Some marine archaebacteria are extreme thermophiles and grow at temperatures of 65- 80$^o$C. 

A plasmid is a small, circular piece of DNA that is different than the chromosomal DNA, which is all the genetic material found in an organism's chromosomes. It replicates independently of chromosomal DNA. Plasmids are mainly found in bacteria.

The archaebacteria are the primitive, single-celled, prokaryotic organisms. These are the ancient and oldest living organisms. These were the first organism which evolved on the Earth. These organisms have evolved to survive in the extreme conditions like the halophiles, thermophiles, acidophiles, methanogens, etc. 

Thermophilic sulphur bacteria are found in hot springs and multiply at temperatutures 100-105$^0$C

The term Obligate anaerobes represent such microorganisms which can survive only in the absence of oxygen, i.e. presence of oxygen in their surrounding environment acts as a poison for them. Methane bacteria also called as methanogens are methane-producing bacteria which are obligate anaerobes as their metabolic processes do not require oxygen. Spirogyra are the green algae which produces oxygen. Pisum Sativum is commonly known as Green pea, which is a vegetable. Onion is also a vegetable.

The correct answer is D. 

Methanogens are responsible for methane gas production in biogas. Methanogen belongs to Archaebacteria class. Archeae are prokaryotic bacteria. They have no cell nucleus. They were initially classified as bacteria and hence called as Archaebacteria. 

• Halophiles are the prokaryotes that can be aerobic or anaerobic. 
• The phototropic anaerobic halophiles can trap solar energy for the synthesis of ATP i.e Adenosine Triphosphate with the help of ATP synthase enzyme. ATP is also known as the energy currency of a cell.
• The correct answer is C.

Methanogens are microorganisms that produce methane in absence of oxygen by the process called as methanogenesis. They belong to the kingdom Monera and the domain archaea. They use inorganic material as the source of energy such as hydrogen sulfide, elemental sulfur, ferrous iron, ammonia. They reduce carbon dioxide to methane and use hydrogen gas as an electron-donating reductant.

Clostridium bacteria is one of the most cause of food poisoning. It is a rod-shaped Gram-positive bacteria. It is a causative agent of botulism disease. It is a gas forming bacteria. It causes causative agent of botulism Gas gangrene by producing gas in tissues in gangrene.

Obligate anaerobes are organisms which grow in absence of oxygen. In presence of oxygen, they cannot survive. The example includes methane producing bacteria or methanogens.  They obtain their energy without consumption of oxygen. Other examples include Clostridium species.

Halophiles are organisms that thrive in high salt concentrations. They are also called as salt-loving microorganisms. Majority of halophiles belongs to Archaebacteria group. They are found in hypersaline environments like in arid, coastal, deep‐sea, underground salt mines. They can comfortably live in evaporation ponds or salt lakes, salt pans and salt marshes. 

There are three major known groups of Archaebacteria, namely methanogens, halophiles and thermophiles. Halophiles are organisms that thrive in high salt concentrations. Thermophiles are organisms that thrive extreme temperatures. Methanogens are organisms that produce methane gas.

Sambhar Salt Lake is India's largest inland salt lake. It is found in the city of Jaipur, state Rajasthan. Hence, the city is also known as Salt Lake City. The water in the lake comes from the rivers Mendha, Runpangarh, Khandel and Karian. 

Monera is non-nucleated unicellular organisms. They are prokaryotes. They have no membrane-bound organelles such as mitochondria, Golgi complex. They lack a true nucleus. Instead, they have nucleoid, genetic material without a nuclear membrane. Examples include Bacteria, Archaebacteria, Mycoplasma, Blue-Green algae. Out of these, the most primitive of monerans are Archaebacteria.

There are three major known groups of Archaebacteria, namely methanogens, halophiles and thermophiles. Halophiles are organisms that thrive in high salt concentrations. They are found in hypersaline environments like in arid, coastal, deep‐sea, underground salt mines. Thermophiles are organisms that thrive extreme temperatures. 

Marsh gas is also called as biogas. It is also called as methane gas as it primarily consists of methane gas along with hydrogen sulfide and carbon dioxide in minor composition. It is a produced by the decomposition of vegetable matter under water by anaerobic bacteria. Bacteria useful in biogas fermentation are Methanogens. They are found in marshes.

Archaebacteria are unicellular prokaryotic organisms. They include halophiles, thermophiles, methanogens. They are found in extreme habitats like areas with high salt concentration, extremely high temperature, marshy areas. They are non-photosynthetic bacteria. They are the oldest living beings. They are primitive organisms.

Halophiles are bacteria that are found in high salt concentration conditions. Examples include Halobacillus, Halococcus. Bacteria found in hot acidic aerobic conditions are called as thermoacidophiles. Examples include Thermoplasma, Thermococci. Methanogens are organisms that produces methane gas. Example includes Methanococcus. Rickettsiae are obligate intracellular, Gram-negative bacteria found in ticks, lice, fleas, mites, mammals. Example includes Rickettsia rickettsii.

Methanogens belongs to Archeabacteria groups. They are involved in the production of methane gas or marshy gas. They are capable of producing methange gas in marshy areas. Examples include Methanococcus, Methanobacterium.

Domains Archaea contains single-celled microorganisms. These are prokaryotes. They do not have a true nucleus or membrane-bound organelles. They lack peptidoglycan in the cell wall. However, they have some novel features absent in other prokaryotes and eukaryotes. Instead of ester bonds like in prokaryotes and eukaryotes, they have ether bonds connecting fatty acids to molecules of glycerol. 

Methanogen belongs to Archaebacteria group. They are capable of producing methane gas or marshy gas or biogas. They produces methane gas in marshy areas. They are most abundant in marshy areas and cattle yard where cow sheds are present. The methange gas produces a peculiar odour in these areas.

Archaebacteria are prokaryotes without true nucleus. They are of mainly 3 types, halophiles, thermophiles and methanogesn. They live in harsh habitat. Halophiles archaebacteria are found in extreme salty areas. Thermophiles are found in hot springs where temperature is extremely high. Methanogens are found in marshy areas and produce methange gas.

• Many thermophiles are archaea, while thermophilic eubacteria are suggested to have been among the earliest bacteria.
•  Many of these require elemental sulfur for growth. Some are anaerobes, that use the sulfur as an electron acceptor during cellular respiration. 
• Some are lithotrophs, that oxidize sulfur to sulfuric acid, thus requiring the microorganism to be adapted to very low pH as well. These organisms are inhabitants of hot, sulfur-rich environments such as hot springs and geysers etc. Option D is correct.

Methanogen belongs to Archaebacteria group. They are capable of producing methane gas or marshy gas or biogas. They produces methane gas in marshy areas and cow sheds. This produces a peculiar odour.

Methanogens belongs to Archaebacteria. They are primitive prokaryotes. They produce methane gas or biogas. They produce biogas or marshy gas from the drug of ruminant animals. They are found in marshy areas and digestive tract of ruminants.

Methanogens belongs to Archaebacteria. The other members of Archaebacteria includes halophiles and thermophiles. These are primitive prokaryotes. Methanogens produce methane gas or biogas. They produce biogas or marshy gas in marshy areas, rice fields and digestive tract of ruminants.

Archeabacteria are also known as extremophiles because of the ability to survive in extreme environmental conditions. The deep sea environment is characterized by increased pressure, low visibility, low in nutrition etc. Benthic zone also harbors bacteria

Archaebacteria are the oldest living organism. They can be found in some of the harshest environments. Traces of Archaebacteria have been seen in 3.8 billion-year-old fossil. Thus, are claimed as the oldest living organism. Heterocysts are nitrogen-fixing cells found in Nitrogen deprived cells of bacteria like cyanobacteria, Anabaena, Nostoc etc. Heterocyst synthesizes additional 3 layers of the cell wall, in turn, producing a THICK cell wall.The cell wall and cell membrane of archaebacteria both differ from that of eubacteria.The antibiotic, penicillin is ineffective against mycoplasma. So, the correct answer is option B.

Haloarchaea are a class of the Euryarchaeota, found in water saturated.

A facultative anaerobe is an organism that makes aerobic respiration if oxygen is absent.

Archaea have rigid cell walls which help in living at a deep-sea vent.

A thermoacidophile is an extremophilic microorganism that is both can grow under conditions of high temperature and low pH.

Thermococcus, Methanococcus and Methanobacterium are archaea whose histones are shorter than eukaryotic histones and are assembled in tetramers.

The bacterial cell is a prokaryotic type of cell which lacks membrane-bound cell organelles.

Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions. Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals. Methanogens are obligate anaerobes.

Paramecium consists cilia on the cell wall which is made up of the pellicle, paramecium does not contain calcium carbonate shell and the food in the paramecium passes through the cell mouth into the gullet.

Methanobacterium is found in the rumen (a part of the stomach) of cattle. A lot of cellulosic material is also available in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in nutrition of cattle.

Methanogens produce methane gas, nostoc fixes atmospheric nitrogen, mycoplasma lacks a cell wall and can survive without oxygen.

Halophiles can be found in a concentration of salt five times greater than the salt concentration of the ocean.

The archaebacteria are the primitive, single-celled, prokaryotic organisms. These bacteria can reproduce through asexual reproduction. The modes of reproduction include binary fission and fragmentation. The cell divides to form two daughter cells through binary fission. The fragments which are produced have the capability to develop into new organisms. 

Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic condition. They include Methanobacterium, Methanobrevibacter and Methanococcus. 

Methanogens are the primitive bacteria belonging to archaea which are able to produce methane. These organisms can utilise the carbon dioxide and hydrogen gas to form methane. These organisms are found in marshy areas where they produce the marsh gas, in swamps and in the stomach of certain animals. These organisms are responsible for methane production in the stomach of cattle which causes belching.

The archaebacteria are the single-celled, prokaryotic organisms. They do not have well-developed organelles and cellular structures. These organisms can survive in extreme conditions like high temperatures, high salt concentration, high temperature, etc. Some organisms from this group can produce methane through the process of methanogenesis. 

Marsh gas is also called as biogas. It is also called as methane gas as it primarily consists of methane gas along with hydrogen sulfide and carbon dioxide in minor composition. It is a produced by the decomposition of vegetable matter under water by anaerobic bacteria. The marsh gas is produced by Methanogens that are found in marshes.

Peptidoglycan is a polymer that is present in the cell wall of most bacteria. It is also called as Murein. However, Archaebacteria are devoid of peptidoglycan in its wall. Instead, they are made up of the polysaccharide called pseudomurein.

Halophiles are organisms that grow in high salt concentrations. They are also called as salt-loving microorganisms. They are found in hypersaline environments like in arid, coastal, deep‐sea, underground salt mines. They can comfortably live in evaporation ponds or salt lakes due to the accumulation of KCl. By accumulating KCl, they maintain the osmotic balance. 

Peptidoglycan is a polymer that is present in the cell wall of most bacteria. It is also called as Murein. However, Archaebacteria are devoid of peptidoglycan in its wall. Instead, they are made up of the polysaccharide called pseudomurein. Arachebacteria consists of 3 groups, namely halophiles, thermophiles and methanogens. 

Archaebacteria are a type of single-cell organism which do not have membrane-bound organelles. They also lack true nucleus. They live in some of the harshest habitats. They have cell wall which is made up of polysaccharides and proteins without peptidoglycan. They include Methanogens, halophiles, thermophiles. Methanogens produce methane gas or biogas. They are present in the gut of several ruminant animals. Halophiles are present in areas with high salt concentrations. Thermophiles are present in areas with extremely high temperature.

Halophiles are organisms that thrive in high salt concentrations. They are also called salt-loving microorganisms. They are found in hypersaline environments like in arid, coastal, deep‐sea, underground salt mines. They can comfortably live in evaporation ponds or salt lakes such as Great Salt Lake, Owens Lake and the Dead Sea. They cannot live in less than 3M NaCl concentration. The concentration higher than 3M NaCl in the environment will cause movement of water outside from a plant cell to the environment and cell will die due to osmotic stress. A concentration of less than 3M NaCl concentration in the environment will cause the movement of water inside the cell from the environment will cause the cell to burst and the plant will die.

Thermococcus, Methanococcus and Methanobacterium are Archaebacteria. They lack histones. They have negatively supercoiled DNA. They differ from bacteria in a way that they survive extreme conditions. Unlike bacteria, archaea cell walls do not contain peptidoglycan. 

Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions.

Methanogens belong to archaebacteria. They are strict anaerobes. They are autotrophs which obtain both energy and carbon from decomposition products. They occur in marshy areas where they convert formic acid and carbon dioxide into methane with the help of hydrogen. This capability is commercially exploited in the production of methane and fuel gas inside gobar gas plants, e.g., Methanobacterium, Methanococcus. Some of the methanogens live as symbionts inside rumen of herbivorous animals that chew their cud. These archaebacteria are helpful to the ruminants in fermentation of celullose.

Trypanosoma parasites cause sleeping sickness or African trypanosomiasis or Chagas disease which is found in sub-Saharan Africa.

Nitrogen fixing is seen in heterotrophic bacteria live in the soil and fix significant levels of nitrogen, species like Clostridium, Bacillus, Azotobacter are called nitrogen-fixing bacteria.

Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain of archaea. They are common in wetlands, where they are responsible for marsh gas, and in the digestive tracts of animals such as ruminants and humans, where they are responsible for the methane content of belching in ruminants and flatulence in humans. In marine sediments the biological production of methane, also termed methanogenesis, is generally confined to where sulfates are depleted, below the top layers. Moreover, the methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments. Others are extremophiles, found in environments such as hot springs and submarine hydrothermal vents as well as in the "solid" rock of the Earth's crust, kilometers below the surface.

A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to respiration if oxygen is absent.

Monera is the unicellular organism's having a prokaryotic cellular structure, these are microorganisms that evolve methane gas are prokaryotic and belong to the domain of archaea, methanogenic archaea are found in the digestive tracts of human beings along with ruminants, termites, and humans.