Identify the salt R from the observation
Salt R is black in colour. On reacting with concentrated HCl, it liberates a pungent greenish yellow gas which turns moist starch iodide paper blue black.

Explanation

To identify the salt R from the given observations, we can follow these steps:

### Step 1: Analyze the Color of the Salt
The problem states that salt R is black in color. This narrows down our options to certain metal oxides, particularly those of manganese.

**Hint:** Consider common black-colored metal oxides when identifying the salt.

### Step 2: Reaction with Concentrated HCl
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