Deuterium resembles hydrogen in properties but :

Solution

Chemistry ma’am · 5 steps

Same electron, so the same kinds of reactions, but double the mass makes deuterium react more slowly.

1. Same electrons. Deuterium has one proton and one electron, just like protium, so both have the configuration 1s¹. Chemistry is decided by electrons, so deuterium undergoes the same kinds of reactions as hydrogen.
2. Different mass. Deuterium also carries one neutron, so it is about twice as heavy. This makes bonds to deuterium slightly stronger. The bond dissociation enthalpy of D₂ is 443.35 kJ mol⁻¹, against 435.88 kJ mol⁻¹ for H₂.
3. Slower reactions. A stronger bond needs more energy to break, so reactions of deuterium go more slowly. This rate difference is called the isotope effect. It is why H₂O is electrolysed faster than D₂O, which lets heavy water collect in the cell.
4. Not radioactive. Deuterium is a stable isotope and emits no particles. Only tritium is radioactive, and it emits β⁻ particles, not β⁺.
5. So. Deuterium resembles hydrogen but reacts slower than hydrogen, which is option (a).

The idea to keep. Isotopes give the same kinds of reactions because they have the same electrons. Mass changes only the speed: the heavier isotope forms stronger bonds and reacts more slowly.

Answer from the NTA final answer key. Solution by PrepWiser.