For an ideal gas obeying Boyle's Law,which of the following is correct? ($K$ is a constant)

If a gas expands from $20 \ cm^3$ to $50 \ cm^3$ at a constant temperature $(T)$ under a pressure of $1 \ atm$,what will be the final pressure?

At constant temperature,in a given mass of an ideal gas,

Assuming ideal gas behaviour,the ratio of density of ammonia to that of hydrogen chloride at the same temperature and pressure is: (Atomic wt. of $Cl = 35.5 \ u$)

$A$ gas at $5 \, bar$ pressure is heated from $0 \, ^\circ C$ to $546 \, ^\circ C$ and its volume is reduced to one-third of its initial volume. Calculate the final pressure. (in $, bar$)

If the volume of $N_2$ gas at $STP$ is $204.75 \, mL$,then calculate the volume of the gas at $1.5 \, bar$ pressure and $127 \, ^oC$ temperature.