Assertion (A): A molar solution is more concentrated than molal solution.
Reason (R): A molar solution contains one mole of solute in 1000 mL of solution.

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 solve the question regarding the assertion and reason about molar and molal solutions, we will analyze both statements step by step.

### Step 1: Understanding Molarity and Molality
- **Molarity (M)** is defined as the number of moles of solute per liter of solution. The formula is:
\[ M = \frac{n}{V} \]
where \( n \) is the number of moles of solute and \( V \) is the volume of the solution in liters.

- **Molality (m)** is defined as the number of moles of solute per kilogram of solvent. The formula is:
\[ m = \frac{n}{W} \]
where \( n \) is the number of moles of solute and \( W \) is the weight of the solvent in kilograms.

### Step 2: Analyzing the Assertion (A)
- The assertion states that a molar solution is more concentrated than a molal solution. To determine if this is true, we need to compare the concentration of both solutions.

### Step 3: Analyzing the Reason (R)
- The reason states that a molar solution contains one mole of solute in 1000 mL of solution. This is indeed correct as it defines a 1 M solution.

### Step 4: Comparison of Concentrations
- Let's assume we have a 1 molal solution (1 m) and a 1 molar solution (1 M). For a 1 molal solution, if we take 1 kg of water (which is approximately 1000 mL), the volume of the solution will be greater than 1000 mL because the solute will occupy some volume.
- Therefore, for a 1 molal solution, the volume of the solution will be slightly more than 1 L (1000 mL) due to the added solute.

### Step 5: Conclusion
- Since the volume of the solution in the case of molality is greater than 1 L, the number of moles of solute in a 1 molal solution will be less than that in a 1 molar solution when both are compared at the same weight of solvent.
- Hence, a 1 molar solution is indeed more concentrated than a 1 molal solution.

### Final Answer
- Both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion.