Find (a) the total number of neutrons and (b) the total mass of neutrons in 7 mg of 14C. [Assume that the mass of a neutron = 1.675 × 10⁻²⁷ kg]

The number of neutrons is equal to the difference in the mass number and atomic number. It is equal to 14 - 6 = 8
(a) The number of neutrons present in 7 mg (7 × 10⁻³ g) of C-14:
= 7 × 10⁻³ × (1/14) × 6.02 × 10²³ × 8 = 2.408 × 10²¹ neutrons
(b) Total mass of neutrons in 7 mg of C-14:
(mass of one neutron = 1.675 × 10⁻²⁷ kg)
= 2.408 × 10²¹ × 1.675 × 10⁻²⁷ = 4.035 × 10⁻⁶ kg