Which of the following statement(s) is not correct?

Options

A. The electronic configuration of Cr is [Ar] `3d^(5) 4s^(1)` (At. No. of Cr= 24).
B. The magnetic quantum number may have a negative, value.
C. In silver atom, 23 electrons have a spin of one type and 24 of the opposite type. (At. no. of Ag =47).
D. The oxidation state of nitrogen in `N_3H` is -3.

Answer

To determine which of the given statements is not correct, we will analyze each option step by step.

### Step 1: Analyze the first statement
**Statement:** The electronic configuration of chromium is Argon 3d⁵ 4s¹.

- **Analysis:**
- The atomic number of chromium (Cr) is 24.
- The electronic configuration is built up from the previous noble gas, Argon (atomic number 18), followed by the filling of the orbitals.
- According to the Aufbau principle and the n + l rule, the configuration for chromium is indeed Argon 3d⁵ 4s¹.
- This is because chromium has a half-filled d-subshell, which provides extra stability. Therefore, this statement is **correct**.

### Step 2: Analyze the second statement
**Statement:** The magnetic quantum number may have negative values.

- **Analysis:**
- The magnetic quantum number (m) can take values from -l to +l, where l is the azimuthal quantum number.
- For example, for a p subshell (l = 1), m can be -1, 0, or +1.
- Hence, it is true that the magnetic quantum number can have negative values. Therefore, this statement is **correct**.

### Step 3: Analyze the third statement
**Statement:** In a silver atom, 23 electrons have a spin of one type and 24 of the opposite type.

- **Analysis:**
- Silver (Ag) has an atomic number of 47, meaning it has 47 electrons.
- According to the Pauli exclusion principle, each orbital can hold two electrons with opposite spins.
- The statement implies an imbalance in the spins of electrons, which is not typical for a neutral atom.
- Therefore, this statement is **incorrect**.

### Step 4: Analyze the fourth statement
**Statement:** The oxidation state of nitrogen in N₃H is -3.

- **Analysis:**
- Let the oxidation state of nitrogen be x.
- For three nitrogen atoms, the contribution is 3x.
- The oxidation state of hydrogen is +1.
- The equation for the neutral compound is: 3x + 1 = 0.
- Solving for x gives x = -1/3.
- Thus, the oxidation state of nitrogen in N₃H is -1/3, not -3. Therefore, this statement is **incorrect**.

### Conclusion
The statements that are not correct are:
- The third statement about the spins of electrons in silver.
- The fourth statement about the oxidation state of nitrogen in N₃H.

### Final Answer
The incorrect statement is: "In a silver atom, 23 electrons have a spin of one type and 24 of the opposite type."