a
Fers $1$ gram mol of a gas,
Ideal gas equation is $P V=R T$
At $NTP$, $P= 1 \; atm =10^{5} N / m ^{2}$
$V= 22.4 L =22.4 \times 10^{-3} m ^{3}$
$T=273 K$
Substitule $R=\frac{\left(10^{5}\right) \times\left(22.4 \times 10^{-3}\right)}{(273)}=8.2 J / K$
Convert into $cal/K$ $R=\frac{8.2}{4.1} cal / K =2 cal / K$
correct option is $(A)$