Question

can someone explain why is the answer c?

Answer 1

one mol of any substance occupies 22.4L at STP.
$that \: means \: 6.022 \times 10 ^{23} \: molecules \: or \: atoms \: occupy \: 22.4 \: litres.$
$if \: 22.4 \: litres \: becomes \: 1.12 \: litres \: it \: decreases \: by \: 20 \: times$
so the answer should be
$6.022 \times 10 ^{23} \div 20 \\ = 3.011 \times 10 ^{22}$