To identify the grammatically correct sentence. Let's analyze each option:

The question asks to identify the grammatically correct sentence. Let's analyze each option:

• (a) I discussed about the issue The verb "discuss" is a transitive verb, which means it takes a direct object. It already implies "to talk about" something. Therefore, using the preposition "about" after "discussed" is redundant and grammatically incorrect.

• (b) I discussed the issue In this sentence, "the issue" is the direct object of the verb "discussed". This is the correct grammatical construction for the verb "discuss".

• (c) I discussed on the issue Similar to option (a), using the preposition "on" after "discussed" is incorrect.

• (d) I discussed over the issue Similar to options (a) and (c), using the preposition "over" after "discussed" is incorrect.

The verb "discuss" does not require a preposition (like "about," "on," or "over") when followed by its object.

The correct sentence is (b).

The final answer is $\boxed{\text{B}}$