Question

find number of hydrogen atom in 4.5 gram of ethane

Answer 1

$0.9 \times 6.022137 \times {10}^{23}$

Answer 2

moles of ethane= 4.5/30=0.15moles
1 mole of ethane contains 6 moles of hydrogen as given by formula c2h6.
now 0.15 mole will contain=
0.15×6×NA
where NA is Avogadro's number.