Question

which of the following is a chemical change?
burning natural gas
melting ice
cutting a tomato
hammering gold into foil

Explanation:

To determine a chemical change, we check for new substance formation.

• Burning natural gas: Natural gas (mostly methane, $\ce{CH4}$) reacts with $\ce{O2}$ to form $\ce{CO2}$ and $\ce{H2O}$, new substances are created.
• Melting ice: Ice (solid $\ce{H2O}$) becomes liquid $\ce{H2O}$; no new substance, just state change (physical).
• Cutting a tomato: Only changes size/shape, no new substance (physical).
• Hammering gold into foil: Changes shape, gold remains gold (physical).

So burning natural gas is a chemical change.

Answer:

burning natural gas