Identify linear molecule from following.

Find the number of moles of $\text{CO}_2$ present in a sample occuping $4 \times 10^{-3}\,\text{m}^3$ at $1.104 \times 10^5\,\text{Nm}^{-2}$ pressure ($R \times T = 2208\ \text{J mol}^{-1}$)

If $2$ mole of an ideal gas expand isothermally and reversibly at $27^\circ$C from 1 $\text{dm}^3$ to $1\ \text{m}^3$ calculate work done? $[R = 8.314\ \text{J K}^{-1}\text{mol}^{-1}]$

Identify the law for the statement "Overall the enthalpy change for a reaction is equal to sum of enthalpy changes of individual steps in the reaction"