Which of the given statement is incorrect ?

Options

A. `He` is used in production of powerful super conducting magnets
B. `He` is used for carrying out experiments at low temperature as a cryogenic agent
C. `He` is used as an inert shield for arc welding
D. `He` is used in filling the gas balloons instead of `H_2` gas, because He is lighter than inflammable

Answer

To solve the question of which statement is incorrect regarding helium, we will analyze each option step by step.

### Step 1: Analyze Option A
**Statement:** Helium is used in the production of powerful superconducting magnets.

**Analysis:**
- Helium is indeed used in the production of superconducting magnets because it has a very low boiling point and can help achieve the low temperatures necessary for superconductivity.
- Therefore, this statement is **correct**.

### Step 2: Analyze Option B
**Statement:** Helium is used for carrying out experiments at low temperature as a cryogenic agent.

**Analysis:**
- Helium is widely used as a cryogenic agent due to its low boiling point, which allows it to remain in a liquid state at very low temperatures.
- This statement is also **correct**.

### Step 3: Analyze Option C
**Statement:** Helium is used as an inert shield for arc welding.

**Analysis:**
- Helium is used as a shielding gas in arc welding to protect the weld pool from atmospheric contamination.
- Since it is an inert gas, it does not react with the materials being welded, making this statement **correct**.

### Step 4: Analyze Option D
**Statement:** Helium is used in filling gas balloons instead of hydrogen gas because helium is lighter and inflammable.

**Analysis:**
- This statement is misleading. While helium is used to fill balloons because it is non-flammable (unlike hydrogen), it is **not lighter than hydrogen**. In fact, hydrogen is lighter than helium.
- Therefore, this statement is **incorrect**.

### Conclusion
The incorrect statement is **Option D**.