One kg of air in a closed system undergoes an irreversible process from an initial state of $p_1=1$ bar (absolute) and $T_1=27^\circ C$, to a final state of $p_2=3$ bar (absolute) and $T_2=127 ^ \circ C$. If the gas constant of air is $287 \: \text{J/kg.K}$ and the ratio of the specific heats $\gamma = 1.4$, then the change in the specific entropy (in $\text{J/kg.K}$) of the air in the process is

1. $-26.3$
2. $28.4$
3. $172.0$
4. indeterminate, as the process is irreversible