(A) bohr's third postulaate states that the stationary orbits are those for which the angular momentum is some integral multiple of `(h)/(2pi)`.
(R) linear momentum of the electron in the atom is quantised.

Options

A. if both assertion and reason are true and reason is the correct explanation of assertion.
B. if both assertion and reason are true but reason is not the correct explanation of assertion.
C. if assertion is true but reason is false.
D. if both assertion and reason are false.

Explanation

To analyze the given statements regarding Bohr's postulates, we will break down the assertion and reason step by step.

### Step 1: Understanding Bohr's Third Postulate
Bohr's third postulate states that the stationary orbits of an electron in an atom are those for which the angular momentum (L) is quantized. Specifically, it is given by the formula:
\[ L = n \frac{h}{2\pi} \]
where \( n \) is a positive integer (the principal quantum number) and \( h \) is Planck's constant.

### Step 2: Evaluating the Assertion (A)
The assertion states that "Bohr's third postulate states that the stationary orbits are those for which the angular momentum is some integral multiple of \( \frac{h}{2\pi} \)." This is indeed true as it directly reflects Bohr's third postulate.

### Step 3: Evaluating the Reason (R)
The reason states that "the linear momentum of the electron in the atom is quantized." In Bohr's model, while angular momentum is quantized, linear momentum is not quantized in the same way. The linear momentum can take a range of values, depending on the velocity of the electron and the radius of its orbit. Therefore, this statement is false.

### Step 4: Conclusion
Since the assertion is true and the reason is false, the overall statement that both the assertion and reason are correct is incorrect.

### Final Answer
The assertion (A) is true, while the reason (R) is false.

---