Final answer:
In a series circuit, the voltage drop across each resistor adds up to the total supply voltage. So, the voltage drop across R2 is 10 volts.
Step-by-step explanation:
In a series circuit, the total voltage across the circuit is equal to the sum of the voltage drops across each component. In this case, the power supply is providing 15 volts, and the voltage drop across R1 is 5 volts. Therefore, the voltage drop across R2 can be found by subtracting the voltage drop across R1 from the total voltage: 15 volts - 5 volts = 10 volts.