$F$ being highly electronegative has the ability to form hydrogen bonds due to which boiling point of $HF$ is high.

The melting point of a compound depends on Vander walls force of attraction which increases as molecular size increases, in given compounds Sr atom has the largest size, so vanderwalls force of attraction will be greater in $SrF _2$ and it will have the highest melting point.

Reactivity oder in halogen is:
$F _2>Cl _2>Br _2>I _2$

Bromine, mercury and gallium exist in liquid state at room temperature

Halogens

$F _{2}$ gas $Cl _{2}$ gas 

When $Br(I)$ goes to to $Br(g)$ then stability of molecules increase. This leads us to negative entropy.

Chlorine is gas, bromine is liquid and iodine is solid.

The ionization energies of halogens decrease on moving down the group.

Boiling point increases with increasing atomic size. $Cl _2$, thus, has the lowest boiling point.

According to the values electron affinity the  three halogens X, Y and Z are $Cl _2$,$F _2$ and $Br _2$

$F _2$ is a smaller molecule than $Cl _2$. This means that the bonded electrons in $F _2$ are closer to the outer shell unbonded electrons. Due to the electron repulsion theory, the bonded electrons repel the outer shell unbonded electrons far more in $F _2$ than they would in $Cl _2$. 

The correct increasing order of the pi bonding tendency is $Si\, -\, O\, <\, P\, -\, O\, <\, S\, -\, O\, <\, Cl\, -\, O$.
This is because, with decrease in the size from Si to Cl, the effectiveness of the sideways overlap increases.

$F _{2}$ - pale yellow colour gas

$Cl _{2}$ - greenish colour gas

$Br _{2}$ - orange liquid

$I _{2}$ - Violet colour solid

A) 1

B) 4

C) 3

D) 2

Iodine has atomic number 53 belonging to group 17. The name is from Greek meaning violet or purple due to the colour of elemental iodine vapour. It is a bluish-black solid with a metallic lustre sublimating into violet-pink gas and colour is due to absorption of visible light by an electronic transition between highest and lowest molecular orbitals.

Bromine is a liquid non-metal because the inter-molecular forces in bromine are very strong and hence it does not vaporise to gaseous form and remains in liquid state itself.

Interhalogen compounds are covalent in nature. More reactive than halogens because of low bond energy due to dissimilar size of atoms in molecule. As the molecule becomes a little polar the boiling point increases due to inter-molecular attraction. They are reactive and unstable because of low bond energy. 

Bromine is the only non metal to exists in liquid state.

Fluorine and chlorine are gases, bromine is a liquid and iodine is solid at STP conditions.

Here, Iodine, bromine, chlorine and fluorine belongs to the same group. The order of their atomic mass are: 

Each halogen has 7 electrons in its outer shell. Atoms are much more stable when they have 8 electrons in their outer shell. The two halogen atoms form a covalent bond with each other to form diatomic molecules in order to complete their octet.

Greenhouse gases are gases in an atmosphere that absorbs and releases radiation This process is the cause of the greenhouse effect. The main greenhouse gases in Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. So $N _2X$ is not greenhouse gas.

Hence option $D$ is correct.

$Br _2$ is the only non-metal which is liquid at room temperature

Option $C$ is the correct answer.

We know that greater the molecular size is; greater will be van der Waal force of attraction between then and higher will be its melting point.

Th tendency to form pi bond increases in the order
$SiO<PO<SO<ClO$
Since the size of Cl tom is smaller compared to Si, P and S, in case of Cl, less internuclear distance results in more effective sideways overlapping.
With increase in the tendency to form  the pi bond, the tendency for polymerization decreases.
Hence, the decreasing order for the tendency for polymerization is $SiO>PO>SO>ClO$.

Only statement I is the true statement. 
Statement I. Fluorine is the most active nonmetallic element in the periodic table.
Statement II. As you move down the family the state of the halogens is from a gas to a solid state.
Thus, fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
Statement III. By filling the outermost p orbital the halogen elements can be converted to ions.

An oxidising agent would displace iodine from potassium iodide. When iodine gets removed, free iodine appears purple in colour.

Statement I : The physical state of halogen molecules may be solids, liquids or gases at room temperature.
Statement 2 : The halogen molecules are considered as nonpolar and by increasing mass the dispersion forces between them increases. With increase in the dispersion forces, the state changes from gas (fluorine and chlorine) to liquid (bromine) to solid (iodine).

Chlorine is a greenish-yellow gas. As we go down the group, the colour of halogens gets darker. Fluorine is pale-yellow in colour, chlorine is greenish-yellow. Bromine is red-brown and iodine is purple.

The halogen with the smallest covalent radius is fluorine.
The halogen with the largest covalent radius is iodine.
The correct order of covalent radii among halogen is fluorine < chlorine <  bromine < iodine.

Since the bond energy of $I _2$ is least, it's bond will be weakest.

Halogens exist as diatomic molecules at room temperature. The valence shell electronic configuration of halogens is  $\displaystyle ns^2 np^5$.  Two halogen atoms share one electron each to form diatomic molecule in which each halogen atom has completed its octet.

$IF _7$ is named as Iodine (VII) Flouride. Because the halogen of larger size give electron pair and the halogen of small size which has high electronegativity accepts a lone pair of electrons. So suffix '-ide' is added to halogen of small size.

Statement 1: Elemental iodine has a higher boiling point than the elemental bromine because of the higher molecular mass of $I _2$ than the $Br _2$.
Statement 2: Iodine does not form stronger covalent bonds than $Br$ because size of iodine is larger due to which the bond becomes longer in length and longer bond is weaker, hence, forms weaker covalent bond.

Statement 1 : Bromine has a higher boiling point than chlorine. This is due to the fact that the Bromine has higher , molar mass than the Chlorine.
Statement 2:
Dispersion forces are present between all molecules, whether they are polar or nonpolar.
Larger and heavier atoms and molecules $(Br)$ exhibit stronger dispersion forces than smaller and lighter ones $ (Cl)$
In a larger atom or molecule, the valence electrons are, on average, farther from the nuclei than in a smaller atom or molecule. They are less tightly held and can more easily form temporary dipoles.
The ease with which the electron distribution around an atom or molecule can be distorted is called the polarizability.
London dispersion forces tend to be:
1. stronger between molecules that are easily polarized.
2. weaker between molecules that are not easily polarized.