The d-block elements are paramagnetic because they

Analyze the question: It asks why d-block elements are paramagnetic, meaning they are weakly attracted to a magnetic field.

Concept:

• Paramagnetism is caused by the presence of unpaired electrons. Each unpaired electron has a magnetic moment (from its spin), so the atom is attracted into a magnetic field.
• Diamagnetism is caused by paired electrons only. Their spins cancel, and the substance is weakly repelled by a magnetic field.

Step-by-step solution:

1. Option A: Paired electrons repelled by a magnetic field describes diamagnetism, not paramagnetism. Wrong.
2. Option B: Unpaired electrons in the partially filled 3d-orbitals. Transition elements such as Fe (3d⁶), Mn (3d⁵), Co (3d⁷) and Cu²⁺ (3d⁹) have partially filled d-subshells with unpaired electrons, so they are attracted to a magnetic field. This is correct.
3. Option C: This is the same idea as A (paired electrons repelled), so it is also diamagnetism. Wrong.
4. Option D: Delocalized valence electrons explain electrical conductivity and metallic bonding, not paramagnetism. Wrong.

Answer: The d-block elements are paramagnetic because they contain unpaired electrons in the partially filled 3d-orbitals.

Exam tip: Remember "Paramagnetic = Presence of unpaired electrons" and "Diamagnetic = Doubled (paired) electrons". If an option mentions paired electrons being repelled, it is describing diamagnetism.