The sources of heat of geothermal energy are which of the following?

1.Radioactive decay of unstable elements

2.Nuclear fusion

3.Magma

4.Temperature gradient inside the earth

5.Oceanic circulation

A1, 2 & 3 only

B2, 3 & 4 only

C1, 3 & 4 only ✓ Correct

D3, 4 & 5 only

Correct answer: (C) 1, 3 & 4 only

Explanation

The heat of geothermal energy comes from radioactive decay, magma and the earth's internal temperature gradient.

Statement 1 is right, as decay of unstable elements releases heat deep within the earth.

Statement 3 is right, as molten magma is a major source of subsurface heat.

Statement 4 is right, as temperature rises steadily with depth inside the earth.

Statement 2 is wrong, because nuclear fusion powers the sun, not the earth's interior.

Statement 5 is wrong, since oceanic circulation moves heat but does not generate geothermal heat.

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