Identify the segment in the sentence, which contains the grammatical error.
No matter he tries hard he cannot play the guitar.

Correct option is B

The issue with (b) "he tries hard" is the missing conjunction. The sentence structure requires a subordinating conjunction like "how" after "No matter" to form a proper clause. The correct phrase should be: "No matter how hard he tries" instead of "No matter he tries hard."
The correct structure should be "No matter how hard he tries" to express that despite his effort, he cannot play the guitar. "No matter" needs to be followed by a clause that begins with "how" to indicate the manner or extent of the action.
Correct sentence: "No matter how hard he tries, he cannot play the guitar."
Thus, the error is in (b) because the conjunction "how" is missing, and the correct phrase should be "No matter how hard he tries."