Assertion (A): Helium used in diving apparatus.
Reason (R): Helium is very less soluble in blood.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is NOT the correct explanation of A
C. A is true but R is false
D. A is false and R is True.

Explanation

To analyze the assertion and reason provided in the question, we can break it down step by step.

### Step 1: Understanding the Assertion
**Assertion (A): Helium is used in diving apparatus.**
- Helium is indeed used in diving equipment, particularly in deep-sea diving. It is preferred over other gases like nitrogen because it helps to prevent conditions such as nitrogen narcosis, which can occur when divers breathe nitrogen at high pressures.

**Hint:** Consider the properties of helium that make it suitable for diving.

### Step 2: Understanding the Reason
**Reason (R): Helium is very less soluble in blood.**
- Helium has a low solubility in blood compared to other gases such as nitrogen. According to Henry's law, the solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid. When divers go deep underwater, the pressure increases, and gases that are more soluble can cause problems like decompression sickness (the bends) when ascending.

**Hint:** Reflect on how gas solubility affects divers' health and safety.

### Step 3: Connecting Assertion and Reason
- The reason provided (R) explains why helium is used in diving apparatus (A). Since helium is less soluble in blood, it reduces the risk of complications associated with gas solubility at high pressures, making it a safer choice for divers.

**Hint:** Think about how the properties of helium directly relate to the safety of divers.

### Step 4: Conclusion
- Both the assertion and the reason are correct, and the reason is a correct explanation of the assertion. Therefore, the correct conclusion is that both A and R are true, and R is the correct explanation of A.

**Final Answer:** Both A and R are true, and R is the correct explanation of A.