A battery of 9 V is connected in series with resistors of 0.2, 0.3, 0.4 , 0.5 and 12 respectively. How much current would flow through the 12 resistor?

All the resistors are connected in series.

Thus, equivalent resistance, R = 0.2 + 0.3 + 0.4 + 0.5 + 12 = 13.4

Potential difference, V = 9 V

And, Current, I=?

Since in series connection, the current throughout the circuit is same. Therefore, 0.67 A will flow through the 12 resistor.