When the value of Kc is very small, it indicates that the equilibrium position of the reaction lies towards the left side, meaning that the concentration of the reactants is relatively high compared to the concentration of the products.

Let's understand this in detail:

Equilibrium Constant (Kc):
The equilibrium constant, Kc, is a measure of the extent of a chemical reaction at equilibrium. It is defined as the ratio of the product concentrations to the reactant concentrations, each raised to their respective stoichiometric coefficients, at equilibrium, with each concentration term raised to the power equal to its stoichiometric coefficient in the balanced chemical equation.

Kc = [Products]^n / [Reactants]^m

Where [Products] and [Reactants] represent the concentrations of the products and reactants at equilibrium, respectively, and n and m are the stoichiometric coefficients of the products and reactants, respectively.

Interpretation of a Very Small Kc Value:
When the value of Kc is very small, it means that the numerator (concentration of products) is much smaller compared to the denominator (concentration of reactants).

This implies that the concentration of the reactants is significantly higher than the concentration of the products at equilibrium.

Explanation of Correct Answer (Option B):
The correct answer, "reactant conc. is maximum," indicates that when the value of Kc is very small, the concentration of the reactants is at its maximum.

This is because the equilibrium position favors the reactants, and the reaction is not proceeding significantly towards the product side. As a result, the concentration of the reactants remains high, while the concentration of the products is relatively low.

In other words, the reaction is not proceeding to a significant extent, and the reactants are dominant in the equilibrium mixture.

Therefore, when the value of Kc is very small, it signifies that the reaction is at the start, and the concentration of the reactants is maximum.