Answer: Option B. -> 12 g
:
B
The chemical formula of methane is $C{H}_4$.The carbon to hydrogen mass ratio in it is $3:1$.
3 gof carbon requires one gram of hydrogen.
So,36 gof carbon requires
=$\frac{36}{3}\times 1=12\text{g}$ of hydrogen

Answer: Option B. -> False
:
B
Law of conservation of mass states that mass can neither be created nor be destroyed in a chemical reaction. In a chemical reaction, physical and chemical properties of matter can be altered but the total massof the matter remains the same.
Since an atom is the basic unit of mass, atoms can neither be created nor be destroyed.

Answer: Option B. -> 11.11%
:
B
Let us consider 1 molecule of $H_{2}O$
Mass of hydrogen in 1 molecule of $H_{2}O$= $2g$
Mass of oxygen in 1 molecule of $H_{2}O$ = $16g$
Therefore, total mass of 1 molecule of $H_{2}O$ = $2+16$ = $18g$
Now percentage of hydrogen is given by:
=$\frac{\text{Mass of hydrogen in 1 molecule of}{H}_{2}O}{\text{Total mass of 1 molecule of}{H}_{2}O}$
=$\frac{2}{18}\times 100=11.11$%

Answer: Option B. -> 3.32×10−23 grams
:
B
1 mole of an element contains $6.022\times {10}^{23}$ atoms.
1 mole of acompound contains$6.022\times {10}^{23}$ molecules.
Neon is monoatomic in nature.
It is given that the gram atomic mass of Neon is 20 g
So, $6.022\times {10}^{23}$ atoms of Neon weigh = 20 grams
The massof one atom
= $\frac{20}{6.022\times {10}^{23}}$
= $3.32\times {10}^{-23}$ g

Answer: Option B. -> Atomic mass unit
:
B
According to IUPAC recommendations, mass of the atom is expressed as atomic mass unit (amu) or unified atomic mass unit (u). 1 amu is defined asone-twelth the mass of a carbon-12 atom.

:
Definition: 2 Marks
Numerical: 3 Marks
Onemoleis defined as the amount of substance containing as many elementary entities (atoms, molecules, ions, electrons, radicals, etc.) as there are atoms in 12 grams of carbon-12. The number of particles that is atoms, ions and molecules present in one mole of a substance is fixed with a value of $6.02\times {10}^{23}$ molecules.
Mole of X element is ;
$nx=(9.03\times {10}^{23}\times (6.02\times {10}^{23})=0.15mol$
Atomic mass of X;
$A_x=\frac{8.4}{0.15}=56g/mol$
Molar mass of $X_2{Y}_3$ compound;
$M_{X_2{Y}_3}=\frac{16}{0.1}=160g/mol$
We find atomic mass of Y by;
2.X + 3Y =160
2.(56) + 3(Y)=160
Y=16g/mol is atomic mass of Y.

:
Each point: 1 Mark
1. The atomic mass is the mass of an atom of a chemical element expressed in atomic mass units. It is equivalent to number of protons and neutrons in the atom.
2. 1 unifiedatomic massunit is defined as $\frac{1}{12}$ of themassof a single carbon-12atom.

:
Each point: 1 Mark
1. Charge on ammonium(${N{H}_4}^{+}$) is +1
2. Charge on sulphate(${S{O}_4}^{2-}$) is -2
3. By cross over charges to balance charges
$(N{H}_4{)}_{2}S{O}_4$.

:
Each point: 1 Mark
1. Atomicity is the total number of atoms present in one molecule of an element or a substance.
2. a. The chemical compound ozone is composed of 3 oxygen atoms. Therefore atomicity is three.
b. The chemical formula of ammonia is ${NH}_3$ in which there are3 Hydrogen atoms and 1 Nitrogen atom.Therefore the atomicity is four.

:
Concept : 1 Mark
Process : 1 Mark
Result : 1 Mark
Carbon and chlorine will combine in such a manner that their valencies should get satisfied.
Valency of Carbon = 4
Valency of Chlorine = 1
To satisfy the valency of Carbon, 4 chlorine atoms each having a valency of 1 would be required. Hence, the formula is $CC{l}_4$