Step 1: Understanding thermosetting polymers.
Thermosetting polymers are polymers that, once set or cured, cannot be remoulded. They are cross-linked and harden permanently upon heating.
Step 2: Analyzing the options.
(A) These are cross-linked polymers: Correct — Thermosetting polymers are typically cross-linked.
(B) These can be remoulded: This is incorrect, as thermosetting polymers cannot be remoulded after curing.
(C) These can be recycled: Incorrect, as thermosetting polymers cannot be recycled easily.
(D) On heating these become soft: Incorrect, as they do not soften on heating once they are cured.
Step 3: Conclusion.
The correct answer is (A) These are cross-linked polymers.