Question

At STP weight of one liter of a gas is $1.25\,g$. The gas will be.
A)${N_2}$.
B)$CO$.
C)${C_2}{H_4}$.
D) All.

Answer 1

The volume occupied by one mole of substance at a given temperature and pressure is called molar volume. It is usually applied to the gases where the nature of the gas does not affect the volume. The most general example is that the molar volume of gas at standard temperature-pressure condition is equal to $22.4\,L$ for one mole of an ideal gas at temperature equal to $273\,K$ and pressure equal to $1\,atm$.

Complete step by step answer:
We know that the atomic mass of an element in grams contains Avogadro’s number of atoms and is defined as the molar mass of that element. To find the molar mass, we have to change the units of atomic mass from the atomic mass unit to grams.
For example, sulfur has an atomic mass of $32\,amu$ so one mole of sulfur has a molar mass of $32\,g$ and contains Avogadro’s number of atoms.
First, we find the molar mass of a gas.
The molar mass of a gas is calculated using the formula:
$Molar{\text{ }}mass{\text{ }} = {\text{ Volume of gas at STP }} \times {\text{ weight of substance}}$
Given,
At STP weight of one liter of a gas is$1.25\,g$.
Thus, the molar mass of the gas is calculated as,
$Molar{\text{ }}mass{\text{ }} = {\text{ }}\;22.4{\text{ }} \times {\text{ }}1.25 = {\text{ }}28{\text{ }}gm$
The molar mass of the gas is $28\,g.$ All the elements in the options have the same molar mass.
Therefore, the option D is correct.

Note:
Now we discuss about the difference between STP and NTP:
Standard temperature and pressure condition is known as STP. The standard temperature value is $0^\circ C$ and the standard pressure value is $100{\text{ }}kPa$ or $1{\text{ }}bar.$ Normal Temperature and Pressure is known as NTP the value of pressure at NTP is $101.325{\text{ }}kPa$ and the temperature at NTP is $20^\circ C$.