Of the following processes in nature, which one involves only a physical change? A. A bird digests a worm. B. Photosynthesis occurs in a leaf. C. An earthquake causes a rockslide. D. A chunk of iron ore rusts.

A physical change is the type of change which does not change the chemical properties of the substance. If an earthquake causes a rockslide in this case the chemical property of the rock still remains the same so it will be a physical change.

All other options are chemical changes because the chemical properties of the substrates will be changed after the completion of process.

When a bird will digest a worm, the proteins of the worm will be broken down into amino acids which will further be converted into energy molecules known as ATP.

During photosynthesis inorganic carbon dioxide & water will be converted into organic bio-molecule known as glucose, the properties of glucose are entirely different from carbon dioxide & water.

Rusting is a chemical process because during rusting iron which is a metal is converted into inorganic molecule iron oxide and the chemical properties of iron oxide are entirely different from iron.