How many times the volume of a diatomic gas should be increased reversibly and adiabatically in order to reduce its $RMS$ velocity to half of its initial value?

For a fixed amount of gas at a constant temperature,which of the following is true?

Which gas has a density of $1.24 \ g/L$ at $0^{\circ} C$ and $1 \ atm$ pressure?

The volume occupied by $4.75 \, g$ of acetylene gas at $50^{\circ} C$ and $740 \, mm \, Hg$ pressure is ....... $L$.
(Rounded off to the nearest integer)
$[$ Given $R = 0.0826 \, L \, atm \, K^{-1} \, mol^{-1} ]$

$2.9 \, g$ of a gas at $95^{\circ} C$ occupied the same volume as $0.184 \, g$ of dihydrogen at $17^{\circ} C$,at the same pressure. What is the molar mass of the gas?

An ideal gas expands isothermally and reversibly from $10 \ m^3$ to $20 \ m^3$ at $300 \ K$,performing $5.187 \ kJ$ of work on the surroundings. Calculate the number of moles of gas used.