Assertion (A): Transition metals are harder than the alkali metals and the alkaline earth metals.
Reason (R): The hardness of transition metals is due to their large atomic size.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is true but (R) is false.
The hardness of a metal depends on the strength of its metallic bonding: the more electrons each atom gives to the metallic bond, the stronger the bonding.
Assertion (A): Transition metals are harder than the alkali metals and the alkaline earth metals. — True. Transition metals (except Zn, Cd and Hg) are very hard, because (n−1)d electrons as well as ns electrons take part in their metallic bonding. Alkali and alkaline earth metals have only one or two ns electrons for metallic bonding, so they are much softer.
Reason (R): The hardness of transition metals is due to their large atomic size. — False. Hardness comes from the strong metallic bonding made by the large number of valence (n−1)d and ns electrons, not from size. Transition metal atoms are in fact smaller than the alkali and alkaline earth metal atoms of the same period.
NCERT (2026-27 edition):
4.3.1 Physical Properties – “The transition metals (with the exception of Zn, Cd and Hg) are very hard and have low volatility. … The high melting points of these metals are attributed to the involvement of greater number of electrons from (n-1)d in addition to the ns electrons in the interatomic metallic bonding.”
“… In general, greater the number of valence electrons, stronger is the resultant bonding.”