Which relation between radioactive heat and density difference is correct in convection current theory?

Correct answer: Heat can create density differences and drive flow

Direct answer: Option A, heat can create density differences and drive flow. In convection theory, internal heat warms material in the mantle. When material becomes hotter, it generally expands and becomes less dense, so it tends to rise. Nearer the cooler upper region, it can lose heat, become denser, and sink. This rising and sinking movement forms convection currents and helps explain mantle movement. Radioactive decay inside Earth is one source of internal heat, although the full heat budget has more than one source. Option A is correct because it connects heat, temperature difference, density difference, and flow. Option B is wrong because heat does not always make density zero; it changes density under particular conditions. Option C is wrong because density differences do not create the Sun. Option D is wrong because radioactive heat is not produced only in oceans; radioactive elements in Earth’s interior and crust contribute to heat. Memory chain: heating → expansion and lower density → rising; cooling → higher density → sinking.