Identify the extensive property amongst the following.

What will be the $\Delta U$ value, when one mole of oxygen $(O_2)$ is heated from $-20^{\circ} C$ to $40^{\circ} C$ at constant volume (in $J$)? (Molar heat capacity for oxygen $\simeq 20.8 \ J \ mol^{-1} \ K^{-1}$)

At constant volume,$4 \; mol$ of an ideal gas when heated from $300 \; K$ to $500 \; K$ changes its internal energy by $5000 \; J$. The molar heat capacity at constant volume is ............... $J \; mol^{-1} \; K^{-1}$

The molar heat capacity of water at constant pressure is $75 \ J \ K^{-1} \ mol^{-1}$. When $1.0 \ kJ$ of heat is supplied to $100 \ g$ of water which is free to expand,the increase in temperature of water is $...... \ K$.

Specific heat capacity is defined as:

$4.48 \ L$ of an ideal gas at $1 \ atm$ and $273 \ K$ requires $12 \ cal$ to raise the temperature by $15 \ ^\circ C$ at constant volume. The $C_p$ of the gas is $... \ cal \ mol^{-1} K^{-1}$.