Explanation

(c)
$Number\ of\ moles\ of\ N_{2} = \frac{56}{28} = 2$
$Number\ of\ moles\ of\ {CO}_{2} = \frac{44}{44} = 1$
$Number\ of\ moles\ of\ {CH}_{4} = \frac{16}{16} = 1$
$\therefore Total\ number\ of\ moles = 2 + 1 + 1 = 4$
$\therefore Mole\ fraction\ of\ {CH}_{4} = \frac{1}{4}$
$\therefore Partial\ pressure\ of\ {CH}_{4}$
$= mole\ fraction\ of\ {CH}_{4}\ \times total\ presure$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{1}{4} \times 720 = 180\ atm$