(i) One gram atom iron = 50 grams

(ii) 5 mole ${\mathrm{N}}_2=5\times 28=140 \mathrm{grams}$

(iii)  ${10}^{24} \mathrm{carbon} \mathrm{atoms} =\frac{12\mathrm{g}}{6.023\times {10}^{23}}={10}^{24}=19.9 \mathrm{grams}$

(iv) 44.8 L of He,  at STP $=\frac{4\mathrm{g}}{22.4\mathrm{L}}\times 44.8\mathrm{L}=8 \mathrm{grams}$

Hence, among given all substances, 5 moles of nitrogen has highest mass.