The number of moles of oxygen in $1 \ L$ of air containing $21 \%$ oxygen by volume,at standard temperature and pressure $(STP)$,is (in $mol$)

How many oxygen atoms are present in $0.36 \ g$ of a drop of water?

The largest number of molecules are in:

Explain the terms: Avogadro constant,molar volume of $1$ mole of gas,and $STP$.

Assertion : Equal moles of different substances contain same number of constituent particles.
Reason : Equal weights of different substances contain the same number of constituent particles.

What is the number of $CO_2$ molecules in $45.42 \ L$ at $\text{STP}$? (Consider molar volume of gas at $\text{STP} = 22.71 \ L \ mol^{-1}$)