The volume of oxygen liberated at STP from 15 mL of 20 volume `H_2 O_2` is

Explanation

To find the volume of oxygen liberated at STP from 15 mL of 20 volume H₂O₂, we can follow these steps:

### Step 1: Understand the concept of "20 volume" H₂O₂
"20 volume" H₂O₂ means that 1 liter (1000 mL) of this solution can liberate 20 liters (20000 mL) of oxygen gas (O₂) when it decomposes.

### Step 2: Calculate the volume of oxygen from 15 mL of 20 volume H₂O₂
We know that 1000 mL of 20 volume H₂O₂ liberates 20000 mL of O₂. Therefore, we can set up a proportion to find out how much O₂ is liberated from 15 mL of H₂O₂.

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