Question

What will be the standard molar volume of He, if its density is 0.1784 g/L at STP?

Answer 1

Try to understand the question and the terms used to avoid confusion. Understand the conditions that are present when STP is mentioned. The conditions in this question means Standard Pressure and Temperature etc.

Complete step by step answer:
We will try to define what STP is to gain a clear understanding of the conditions present.
STP stands for Standard Temperature and Pressure.
Standard Temperature is 0$^\circ$C or 273.15 K.
Standard Pressure is 1 atm or 76 cm of Hg or 101.325 kPa
To avoid the interference of Temperature and pressure in our calculation reactions are performed at STP.
The molar mass of He at STP is 4 amu (atomic mass unit) which is also referred to as 4g.
We have studied in previous classes that 1 mole of any substance occupies 22.4 L of volume at STP. This is also referred to as standard molar volume. So, the standard molar volume of He at STP is 22.4 L.

Therefore, the correct answer is option (B).

Note: When you see the value of density and mass not being mentioned, do not assume any random value, instead read the question carefully. You will get to know that the value of density is not needed as molar volume stays constant.