Three capacitors each of capacitance C and of breakdown voltage V are joined in series. The capacitance and break down voltage of the combination will be

Equivalent capacitance of 'n' identical capacitors in series $=\frac{\mathrm{C}}{\mathrm{n}}\therefore {\mathrm{c}}_{\mathrm{s}}=\frac{\mathrm{C}}{3}$

If potential of 3V is applied across the combination, then each capacitance will have potential V across them. Increasing the net potential across combination more than 3V will break all capacitors.