Question

Number of valency electrons in 4.2 gram of N₃⁻ ion is
(a) 4.2 NA (b) 0.1 NA (c) 1.6 NA (d) 3.2 NA

Answer 1

Answer:

c is right answer.

Explanation:

c it is right answer in my school.

Answer 2

Number of valency electrons in 4.2 gram of N₃⁻ ion is 1.6 NA

Explanation:

Number of valency electrons can be calculated from number of moles and Avogadro number.

• Number of valence electrons in one Nitrogen atom = 5
• Thus, Number of valence electrons in 3 Nitrogen atoms = 15
• Therefore Number of valence electrons in $N_3^-$ ion = 15+1 = 16
• Molecular mass of Nitrogen atom = 14
• Thus, Molecular mass of $N_3^-$ ion = $14 \times 3 = 42$  
• We know, that Number of moles = $\frac{Mass}{Molecular\,mass}$
• Therefore, Total number of valency electrons in 4.2 grams of $N_3^-$ ion = $\frac{4.2}{42} \times 16 \times NA$  
• $=0.1\times 16 NA = 1.6 NA$