Dear student,

Mass of one electron = 9.1 x (1/10³¹) Kg = 9.1 × (1/10²) g

Number of electrons present in a body of 5 nano grams = (5 × (1/10))/(9.1 × (1/ 10²))

= 0.5494 × 10¹

= 5.49×10¹

Therefore, 5.49 × 10¹ electrons should be added into a body to make it heavier by 5 nanograms.

I hope this information was helpful to you.

Good Luck!!