Compared with the mass defects in a nuclear reaction, the mass defects involved in a chemical reaction are
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → almost a million times smaller
Option (1) zero, because mass is conserved in a chemical reaction — Incorrect. Chemical binding energy also lowers the mass of an atom or molecule a little. So a very small mass change does take place in a chemical reaction.
Option (2) about the same as in a nuclear reaction — Incorrect. Energies in chemical reactions are a few electron volts, while nuclear reactions give energies of the order of MeV. The mass changes differ by the same large factor.
Option (3) almost a million times larger — Incorrect. This puts the comparison the wrong way round. Nuclear reactions involve the larger energies, so they have the larger mass defects.
Option (4) almost a million times smaller — Correct. The mass change in a chemical reaction is so small that many people think no mass is converted at all.
NCERT (2026-27):
Example 13.4 – “… However, the mass defects involved in a chemical reaction are almost a million times smaller than those in a nuclear reaction.”