Question

The volume occupied by $7grams$ of nitrogen gas at STP is:
A.$5.6L$
B.$11.2L$
C.$22.4L$
D.$44.8L$

Answer 1

Hint: The volume of one mole of substance at STP (standard temperature and pressure) is $22.4L$ and one mole of substance has $6.022 \times {10^{23}}$ molecules. And the number of moles is equal to the ratio of mass of substance to molecular weight of substance.

Complete step by step answer:
First of all we will talk about the gram molecule, Avogadro number and atoms.
1.Atoms: It is the smallest unit of an element. The elements are made of the same kind of atoms. In the atoms there are three particles: electrons, protons and neutrons.
2.Electrons: They are the negatively charged particle having negligible mass. They move in the atoms outside the nucleus in a fixed orbit.
3.Protons: They are positively charged particles. They have mass. They are present in the nucleus
4.Neutrons: They have no charge but they have mass. They are also present in the nucleus along with protons.
5.Gram molecule: It is defined as the number of grams of the substance i.e. the molecular mass of the substance.
6.Atomic mass: It is defined as the total number of protons and neutrons present in the nucleus of an atom. It is represented by symbol A.
7.Atomic number: It is defined as the number of protons in the nucleus of an atom. It is represented by symbol Z.
8.Molecular weight of the substance: It is defined as the sum of the molecular masses of all elements present in the substance.
9.Number of moles: It is defined as the ratio of mass of the substance to the molecular mass of the substance.
The volume of one mole of substance at STP (standard temperature and pressure) is $22.4L$.
Here in the question we are given with the $7grams$ of nitrogen gas. The molecular weight of nitrogen gas is $28$ because nitrogen gas is ${N_2}$ and the molecular weight of one nitrogen atom is $14$
So the number of moles of nitrogen gas is $\dfrac{7}{{28}} = \dfrac{1}{4}$.
We know that the volume of one mole of substance at STP (standard temperature and pressure) is $22.4L$ then the volume of $\dfrac{1}{4}$ moles of gas at STP will be $\dfrac{1}{4} \times 22.4 = 5.6L$.

So option A is correct.

Note:
 Standard temperature and pressure (STP) is defined as the state where temperature is ${0^ \circ }C$ i.e. $273.15K$ and pressure is $1atm$ i.e. \[760mm{\text{ Hg}}\]. And normal temperature and pressure (NTP) is defined as the state where temperature is ${20^ \circ }C$ i.e. $293.15K$ and pressure is $1atm$ i.e. \[760mm{\text{ Hg}}\].