Neutron is a neutral particle.

in 1932, James Chadwick discovered neutron.

According to Chadwick, neutron is not not found in hydrogen.

The option (C) is the correct answer.
$\displaystyle _{7}{X}^{15}$ and $\displaystyle _{8}{Y}^{15}$ differ in number of neutrons.
Number of neutrons for $\displaystyle _{7}{X}^{15} = 15-7=8$
Number of neutrons for $\displaystyle _{8}{Y}^{15}=15*8=7$
Note: Number of neutrons $\displaystyle =$ mass number $\displaystyle -$ atomic number.

The available hydrogen state ${ H } _{ 1 }^{ 1 }$. It is made of 1 electron, 1 proton and no neutrons. All other elements including isotopes of Hydrogen have neutrons.

Atomic number =$ P =8$ 

The charge to mass ratio is highest for electron.
Charge/mass for :
$neutron=0/1=0, : \ $

Proton have a positive charge and mass equal to one.
neutron have a zero charge and mass equal to one.
Electron have a negative charge and mass equal to 1/1840.

Neutron is heaviest subatomic particle among the given subatomic particles with mass of 1.008 amu while proton have mass of 1 amu.

The statement, 'Neutron can be found in all atoms' is false.

Neutrons are better projectiles than protons.
The decreasing order of the projectile power is $\displaystyle _0n^1 > _{1}H^{1} > _{1}H^{2}> _{2}He^{4}$
The neurons being neutral do not experience repulsion from positively charged nucleus.
Thus, (A) is incorrect, but (R) is correct.

$\displaystyle n< \alpha < p< e$            

Neutron has greatest mass. Proton is a subatomic particle with symbol p and positive electric charge of +1 elementary charge and mass slightly less than that of neutron. Mass of neutron is $1.6749\times10^{-27}  kg$.

Isotone of an element has same no. of neutrons

The triad of nuclei that is isotonic is  $^{14} _6C,\,^{15} _7N,\, ^{17} _9F$.
Number of neutrons are
$C -14-6=8$
$N-15-7=8$
$F-17-9=8$

Two nuclides are isotones if they have same neutron number but different proton number e.g. $boron-12$ and $carbon-13$ both contain 7 neutrons so they are $isotones$.

The two or more species of atoms or nuclei that have the same number of neutrons are called as isotones.

Two nuclides are isotones if they have the very same neutron number but different proton number.

$Atomic\quad radius\quad of\quad neutron\quad =\quad { 10 }^{ -13 }cm\ mass\quad of\quad neutron\quad =\quad 1.6749\times { 10 }^{ -27 }kg\ density\quad of\quad neutron\quad =\quad \dfrac { Mass }{ Volume } =\quad { 10 }^{ 12 }\quad kg/cc$

Helium has 2 neutrons. The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Since, the number of protons present in helium is 2 and given mass is 4. Therefore, the number of neutrons will be equal to $2$ i.e. $4-2.$

The atomic mass of carbon is $12$. The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Since, the number of protons and neutrons present in carbon is $6$.
Therefore, the atomic mass of carbon is $12$ i.e. $6 + 6=12$.

The atomic number of oxygen is 8. The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Also, atomic number is the number of protons present in the nucleus. Since, the number of neutrons present in oxygen is 8 and given mass is 16. Therefore, the number of neutrons will be equal to $8$ i.e. $16-8$.

Neutron has closest mass to a proton. The mass of proton and neutron are 1.0073 amu and 1.0087 amu respectively. Mass of electron is much lower than that of proton and neutron

 The ratio of neutrons in $\displaystyle {O}^{16}$ and $\displaystyle {O}^{18}$ is $\displaystyle 4 : 5 \text { or } 8 : 10$
Number of neutrons in $\displaystyle {O}^{16} = 16-8=8$
Number of neutrons in $\displaystyle {O}^{18}=18-8=10$

 The number of neutrons is the difference between the mass number and atomic number.
   
$\displaystyle _{92}^{235}{U}$ contains the least number of neutrons

The number of neutrons in $\displaystyle _{92}^{235}{U}$ $\displaystyle = 235-92=143$

The number of neutrons in $\displaystyle _{92}^{238}{U} $ $\displaystyle =238-92=146$

The number of neutrons in $\displaystyle _{93}^{239}{Np}$ $\displaystyle = 239-93=146$

The number of neutrons in  $\displaystyle _{93}^{240}{Np}$ $\displaystyle =240-93=147$

The discovery of neutron came very late because it does not carry any charge.

Neutron was discovered by Chadwick.

The mass of neutron is of the order of $\displaystyle {10}^{-27} kg$

It is equal to $\displaystyle 1.674 \times {10}^{-27} kg$ or $\displaystyle 1.674 \times {10}^{-24} g$. It is also equal to 1.0087 amu.

Neutrino has charge 0, mass 0. It was postulated by Fermi in 1934.

The mass defect for $\displaystyle _3^7Li$  is $\displaystyle \Delta m = 0.042$  amu.
1 amu $\displaystyle =931.5$ MeV
Binding energy $\displaystyle = 0.042 \times 931.5 = 39.123$ MeV
Total number of nucleons in $\displaystyle _3^7Li$  is 7 (3 protons and 4 neutrons).
Binding energy per nucleon $\displaystyle =  \dfrac {39.123}{7} = 5.6$ MeV.

The introduction of a neutron into the nuclear composition of an atom would lead to a change in its atomic mass.
However, its atomic number, the chemical nature of the atom and the number of the electron s will remain unchanged as they are related to the number of protons and are independent of the number of neutrons.

Note: The atomic mass is equal to the sum of the number of protons and the number of neutrons. Chemical properties depends on number of electrons which are equal to number of protons in neutral atom. They are also equal to atomic number.

$Radius\ of\ neutron = 1\times 10^{-13}$
$\therefore$ volume $=\dfrac{4}{3}\times \pi  r^{3} = \frac{4}{3}\times \pi (1\times 10^{-13})^{3} = \dfrac{4}{3}\times \pi \times 10^{-39}$
Mass of neutron $=1.6\times 10^{-27}$
$\therefore$ Density $=\dfrac{mass}{volume}$ $=\dfrac{3\times 1.6\times 10^{-27}}{4\times \pi \times 10^{-39}} = \dfrac{4.8}{4\times \pi }\times 10^{12}$ kg/cc

If A = Atomic mass, Z = Atomic number then the number of neutrons is equal to: 

Neutron is neutral sub atomic particle.

Neutron has zero unit charge.
The neutron is a subatomic particle, symbol n or $n^0$, with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with mass approximately one atomic mass unit, constitute the nucleus of an atom, and they are collectively referred to as nucleons

Neutrons are neutral particles. Thus, they are not affected by the electric field.

Gamma rays and neutrons have no charge as they are neutral, hence, these would not be attracted or deflected while traveling through an electric field.

Doubly magic nucleus is $\displaystyle _{ 82 }^{ 208 }{ Pb }$. It has 82 protons and $\displaystyle 208-82=126$ neutrons. 82 and 126 are magic numbers.