Major product in nitration My approach was that when the carbon attached was a secondary one, it would have a greater inductive effect compared to the primary one.

Why is the answer 3? Is it due to steric reasons or am I missing some other factor?
Read this first: Why methyl group is 2,4-directing?

From that answer, we understand that methyl groups (or alkyl groups in general) are o/p directing because of hyperconjugation, and not inductive effects! In fact, as you may also know, inductive effects are generally overshadowed by hyperconjugative effects.

The aromatic ring on the left is more activated because it has two alpha hydrogens - implying more number of hyperconjugative structures - as opposed to only one for the right aromatic ring (a small difference, but good enough for elementary level questions). Thus nitration takes place at the para position of the left ring.