(a) Number of atoms of ^{14}C in 1 mole= 6.023 × 10^{23}

Since 1 atom of ^{14}C contains (14 – 6) i.e., 8 neutrons, the number of neutrons in 14 g of^{ 14}C is (6.023 × 10^{23}) ×8. Or, 14 g of ^{14}C contains (6.022 × 10^{23} × 8) neutrons.

Number of neutrons in 7 mg

6.022*10^{23}*8*7 mg/1400 mg

= 2.4092 × 10^{21}

(b) Mass of one neutron = 1.67493 × 10^{–27} kg

Mass of total neutrons in 7 g of ^{14}C

= (2.4092 × 10^{21}) (1.67493 × 10^{–27} kg)

= 4.0352 × 10^{–6} kg