The volume and temperature of air (assumed to be an ideal gas) in a closed vessel is $2.87 m^{3}$ and $300 \: K$, respectively. The gauge pressure indicated by a manometer fitted to the wall of the vessel is $0.5$ bar. If the gas constant of air is $R=287 \: J/kg.K$ and the atmospheric pressure is $1$ bar, the mass of air (in $kg$) in the vessel is

1. $1.67$
2. $3.33$
3. $5.00$
4. $6.66$