GATE CSE 2026 Session 2 Q29: Which of four grammars are ambiguous

Which of the following grammars is/are ambiguous?

Try it: multiple select: one or more correct options

Select all correct options. No negative marking, no partial marks.

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Answer: B, C (official GATE 2026 final answer key)

Concept used: A grammar is ambiguous if some string has two distinct parse trees (or leftmost derivations).

First step: Try a short string such as $a$ in grammar C, or $id + id * id$ in grammar B, and look for two derivations.

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Source: official GATE 2026 Session 2 CS question paper and final answer key, organised by IIT Guwahati. Question paper · Answer key