Equivalent Capacitance: For capacitors connected in series, the reciprocal of the equivalent capacitance ($C_{eq}$) is the sum of the reciprocals of the individual capacitances [NCERT Class 12, Sec 2.14.1, Eq. 2.45]. $\frac{1}{C_{eq}} = \frac{1}{C} + \frac{1}{C} + \frac{1}{C} = \frac{3}{C}$ $C_{eq} = \frac{C}{3}$

Breakdown Voltage: In a series combination, the total potential difference (voltage) is the sum of the potential differences across each capacitor ($V_{total} = V_1 + V_2 + V_3$). Since the capacitors are identical, the voltage distributes equally. If each capacitor can withstand a maximum voltage $V$ before breaking down, the combination can withstand a total voltage of $V + V + V = 3V$.