When…………..acts on a system of particles, then………….of the system remains…………… .

Explanation

To solve the question, we need to fill in the blanks based on the principles of rotational motion and angular momentum. Here’s the step-by-step solution:

### Step 1: Identify the Condition
We start by identifying the condition under which the system of particles is being analyzed. The key phrase is "when no external torque acts on a system of particles."

**Fill in the first blank:**
"When **no external torque** acts on a system of particles..."

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