### **Official Solution & Step-by-Step Derivation (GATE PH 2022 Q.1)**
**1. Question Analysis & Linguistic Relation**:
- **Prompt**: "You should _________ when to say _________."
- **Context**: The sentence requires a verb denoting cognition/awareness followed by a noun/adverb denoting refusal or negation.
**2. Detailed Step-by-Step Derivation**:
- **Grammatical and Phonetic Analysis**:
- The first blank requires a transitive verb after the modal auxiliary "should": $\text{know}$ (to possess knowledge or discernment).
- The second blank represents the object of the verb "say": $\text{no}$ (an exclamation or expression of refusal/denial).
- Both words are homophones ($/no\mho/$), making this a classic homophonic wordplay question.
- **Option Breakdown**:
- **(A) no / no**: "no" cannot function as a base verb following "should".
- **(B) no / know**: Reverses the required syntactic roles.
- **(C) know / know**: Redundant repetition; "say know" is ungrammatical.
- **(D) know / no**: Syntactically and semantically correct: "You should know when to say no."
**3. Official Verification**:
The verified official IIT Master Answer is **Option (D)** (`know / no`).
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