On increasing the concentration of reactants in a reversible reaction, then equilibrium constant will

The correct option is unchanged.

Understanding the Equilibrium Constant:
The equilibrium constant (represented as $K_c$) for a reversible chemical reaction is a thermodynamic property. For a general reversible reaction at equilibrium:
$aA+bB\rightleftharpoons cC+dD$
The equilibrium constant expression is defined by the ratio of the concentrations of products to reactants, each raised to the power of their stoichiometric coefficients:
$K_c=\frac{{\left[C\right]}^c{\left[D\right]}^d}{{\left[A\right]}^a{\left[B\right]}^b}$
where the square brackets denote equilibrium concentrations.

Effect of Changing Concentration:
When you increase the concentration of the reactants (such as A or B), the system is temporarily disturbed and is no longer at equilibrium. The reaction quotient (Q) becomes less than the equilibrium constant ($Q<K_c$).
According to Le Chatelier's principle, the system will counteract this disturbance by shifting the equilibrium position in the forward direction. This consumes the excess reactants and generates more products until a new equilibrium is established.
At the new equilibrium, even though the individual concentrations of reactants and products are different from their initial equilibrium values, their ratio as defined by the equilibrium expression remains constant. Therefore, the value of $K_c$ does not change.

Conclusion:
The equilibrium constant is a constant at a given temperature. The only factor that can alter the value of the equilibrium constant ($K_c$) for a specific reaction is a change in temperature. Changes in concentration, pressure, volume, or the addition of a catalyst have no effect on the equilibrium constant itself.