Which of the following is true ?

Options

A. Neutrino is a positively charged electron
B. The magnetic moment of an atom is related to the number of unpaired electron in its electronic configuration
C. Bohr theory can be succesifully modified to explain the electronic spectrum of multielectron atom
D. The angle momentum of an eklectron in an atom is gives by `n ((h)/(2pi))`

Explanation

To determine which of the statements given in the question is true, we will evaluate each statement one by one.

### Step 1: Evaluate the first statement
**Statement:** Neutrino is a positively charged electron.

**Evaluation:** Neutrinos are elementary particles that are neutral, meaning they have no charge. They are not electrons, and they do not carry any positive or negative charge. Therefore, this statement is **incorrect**.

### Step 2: Evaluate the second statement
**Statement:** The magnetic moment of an atom is related to the number of unpaired electrons in its electronic configuration.

**Evaluation:** The magnetic moment (μ) of an atom can indeed be calculated using the formula:
\[ \mu = \sqrt{n(n + 2)} \]
where \( n \) is the number of unpaired electrons. This indicates that the magnetic moment is directly related to the number of unpaired electrons. Therefore, this statement is **correct**.

### Step 3: Evaluate the third statement
**Statement:** Bose theory can be successfully modified to explain the electronic spectrum of the multi-electron atom.

**Evaluation:** Bose-Einstein statistics primarily apply to systems of indistinguishable particles and are typically used to describe systems of bosons. However, the theory does not adequately explain the electronic spectra of multi-electron atoms, which require more complex quantum mechanical treatments. Therefore, this statement is **incorrect**.

### Step 4: Evaluate the fourth statement
**Statement:** The angular momentum of an electron is given by \( \frac{nh}{2\pi} \).

**Evaluation:** The correct formula for the orbital angular momentum (L) of an electron in an atom is:
\[ L = \sqrt{l(l + 1)} \frac{h}{2\pi} \]
where \( l \) is the azimuthal quantum number. The statement provided is not entirely accurate as it does not specify the azimuthal quantum number. Therefore, this statement is **incorrect**.

### Conclusion
After evaluating all the statements, we find that the only true statement is the second one: **The magnetic moment of an atom is related to the number of unpaired electrons in its electronic configuration.**

---