The reaction given in (c) will have appreciable concentration of

reactants and products whose K_c are 1.8.

Explanation:

If the value of K_c lies between 1 × 10^-3 and 1 × 10³, a reaction has an appreciable concentration of reactants and products.

⇒In reaction (A),

Cl₂ (g) ⇌ 2Cl (g)

K_c= 5 ×10^–39 (given)

The value of K_c does not lie between 1× 10^-3 and 1× 10³ Hence, this reaction has not the appreciable concentration of reactants and products.

⇒In reaction (B),

Cl₂ (g) + 2NO (g) ⇌ 2NOCl (g)

K_c = 3.7 × 10⁸ (given)

The value of K_c does not lie between 1× 10^-3 and 1×10³ Hence, this reaction has not appreciable concentration of reactants and products.

⇒In reaction (B),

Cl₂ (g) + 2NO₂ (g) ⇌ 2NO₂Cl (g)

K_c = 1.8 (given)

The value of K_c lies between 1× 10^-3 and 1×10³.Hence, this reaction has appreciable concentration of reactants and products.

Note: If K_c > 10³, products predominate over reactants, i.e., if Kc is very large, the reaction proceeds nearly to completion.

If Kc < 10^–3, reactants predominate over products, i.e., if Kc is very small, the reaction proceeds rarely.