Question

how is concentration of hydroxide ions affected when a base is diluted

Answer 1

When an base is diluted, then the concentration of hydrxide ions decreases. This is because on dilution the overall volume of solution increases and so the number of hydroxide ions per unit volume decreases.

@skb

Answer 2

$\large\bf\color{Red}{Hey\: Friend}$

Whenever a base is diluted then the concentration of OH- ion ( hydroxide ion ) decreases. This is because when a base is diluted its pH becomes low due to which the hydroxide ion also become low. This is because concentration of hydroxide ion decrease when the pH value is decreased of a solution and the concentration of hydronium ion increases.