Assertion Second orbit circumference of hydrogen atom is two times the de-Broglie wavelength of electrons in that orbit
Reason de-Broglie wavelength of electron in ground state is minimum.

Options

A. If both Assertion and Reason ar true and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are true but Reason is not correct explanation of Assertion
C. If Assertion is true by Reason is false.
D. If Assertion is false but Reason is true.

Explanation

To solve the assertion-reason question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that the circumference of the second orbit of a hydrogen atom is two times the de-Broglie wavelength of the electron in that orbit.

According to Bohr's model of the hydrogen atom, the circumference of the orbit is given by:
\[ C = 2\pi r \]
where \( r \) is the radius of the orbit.

The de-Broglie wavelength (\( \lambda \)) of an electron is given by:
\[ \lambda = \frac{h}{p} \]
where \( h \) is Planck's constant and \( p \) is the momentum of the electron.

For an electron in the nth orbit, the relationship between the circumference and the de-Broglie wavelength is:
\[ n \lambda = 2\pi r \]

For the second orbit (n=2):
\[ 2\lambda = 2\pi r \]
This confirms that the circumference of the second orbit is indeed twice the de-Broglie wavelength of the electron in that orbit. Therefore, the assertion is **true**.

### Step 2: Understand the Reason
The reason states that the de-Broglie wavelength of the electron in the ground state is minimum.

In the ground state (n=1), the radius of the orbit is at its minimum value. The de-Broglie wavelength in this state can be calculated using:
\[ 2\pi r = n\lambda \]
For n=1:
\[ 2\pi r_1 = \lambda \]
This indicates that the de-Broglie wavelength is at its minimum value when n=1, as the radius \( r_1 \) is also minimum.

Thus, the reason is also **true**.

### Step 3: Determine the Relationship Between Assertion and Reason
While both the assertion and reason are true, the reason does not explain the assertion. The assertion is specifically about the second orbit, while the reason pertains to the ground state.

### Conclusion
Based on the analysis:
- Both assertion and reason are true.
- The reason is not the correct explanation for the assertion.

Thus, the correct answer is:
**Option B: Both assertion and reason are true, but reason is not the correct explanation.**