Assertion (A): Many compounds of the transition metals are paramagnetic.
Reason (R): Many transition metal ions have unpaired electrons in their d orbitals.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Assertion (A) and Reason (R) are correct and Reason (R) is the correct explanation of Assertion (A).
A paramagnetic substance is attracted by a magnetic field; a diamagnetic substance is repelled by it.
Assertion (A): Many compounds of the transition metals are paramagnetic. — True. Transition metals and their compounds show paramagnetic behaviour; for example, \( \ce{Mn^2+} \) (3d5) and \( \ce{Cu^2+} \) (3d9) compounds are attracted by a magnetic field.
Reason (R): Many transition metal ions have unpaired electrons in their d orbitals. — True. With partly filled d orbitals (d1 to d9), most of these ions keep one or more electrons unpaired; only ions such as \( \ce{Sc^3+} \) (3d0) and \( \ce{Zn^2+} \) (3d10) have none.
Why Reason (R) explains Assertion (A)?
Each unpaired electron has a magnetic moment from its spin, and this is what makes a substance paramagnetic.
The ions with unpaired d electrons are therefore the reason the compounds are paramagnetic, so R is the correct explanation of A.
NCERT (2026-27 edition):
4.2 Electronic Configurations of the d-Block Elements – “… With partly filled d orbitals these elements exhibit certain characteristic properties such as display of a variety of oxidation states, formation of coloured ions and entering into complex formation with a variety of ligands. The transition metals and their compounds also exhibit catalytic property and paramagnetic behaviour.”
4.3.9 Magnetic Properties – “… Diamagnetic substances are repelled by the applied field while the paramagnetic substances are attracted. … Many of the transition metal ions are paramagnetic. Paramagnetism arises from the presence of unpaired electrons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum.”