Which of the following is true for the gaseous state?

Under the same conditions of pressure and temperature,the same volume of two gases $A$ and $B$ diffuse through a porous partition in $20 \ s$ and $10 \ s$ respectively. The molecular mass of $A$ is $49 \ u$. The molecular mass of $B$ will be ............. $u$.

What is the density of water vapour at the boiling point of water?

Which one of the following statements is wrong for gases?

Hydrogen gas diffuses $4$ times faster than a mixture of $C_2H_4$ and $CO_2$. Find the molar ratio of $C_2H_4$ and $CO_2$ in the mixture.

Fill in the blanks:
$(1)$ The forces of attraction and repulsion between molecules and atoms are called ....... .
$(2)$ The attractive intermolecular forces between molecules of a substance are also known as .............. .
$(3)$ London forces are also known by the name of ........... .
$(4)$ The mathematical form of Charles's Law is ........ .