The total number of valence electrons in `4. 2g` of ` N_3^-` ion are :

Options

A. ` 2. 2N`
B. ` 4. 2N`
C. `16N`
D. `3.2 N`

Explanation

To find the total number of valence electrons in the \( N_3^- \) ion from \( 4.2 \, g \) of it, we can follow these steps:

### Step 1: Determine the number of valence electrons in one nitrogen atom.
Each nitrogen atom has 5 valence electrons.

**Hint:** Remember that the group number of nitrogen in the periodic table indicates the number of valence electrons.

### Step 2: Calculate the total number of valence electrons in the \( N_3 \) molecule.
Since there are 3 nitrogen atoms in \( N_3 \):
\[ \text{Total valence electrons in } N_3 = 3 \times 5 = 15 \]

**Hint:** Multiply the number of nitrogen atoms by the valence electrons per nitrogen atom.

### Step 3: Account for the charge of the ion.
The \( N_3^- \) ion has an additional electron due to its negative charge:
\[ \text{Total valence electrons in } N_3^- = 15 + 1 = 16 \]

**Hint:** A negative charge indicates that there is one extra electron contributing to the total count.

### Step 4: Calculate the molar mass of \( N_3^- \).
The molar mass of nitrogen (N) is approximately \( 14 \, g/mol \). Therefore, the molar mass of \( N_3 \) is:
\[ \text{Molar mass of } N_3 = 3 \times 14 = 42 \, g/mol \]

**Hint:** Use the atomic mass of nitrogen to find the molar mass of the molecule.

### Step 5: Determine how many moles of \( N_3^- \) are in \( 4.2 \, g \).
Using the molar mass calculated:
\[ \text{Moles of } N_3^- = \frac{4.2 \, g}{42 \, g/mol} = 0.1 \, mol \]

**Hint:** The number of moles can be found using the formula: moles = mass (g) / molar mass (g/mol).

### Step 6: Calculate the total number of valence electrons in \( 4.2 \, g \) of \( N_3^- \).
Since each \( N_3^- \) ion has 16 valence electrons:
\[ \text{Total valence electrons} = 0.1 \, mol \times 16 \, \text{valence electrons} = 1.6 \, \text{valence electrons} \]

**Hint:** Multiply the number of moles by the number of valence electrons per mole to find the total.

### Final Answer:
The total number of valence electrons in \( 4.2 \, g \) of \( N_3^- \) is \( 1.6 \).

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