Question

1. a change in ______ means that a chemical reaction has occurred. (1 point)

the energy and kinds of atoms of the reacting substances
the energy and mass
the kinds of atoms involved
the properties and identity of the reacting substances

Explanation:

A chemical reaction is characterized by a transformation that changes the properties and identity of the reacting substances. According to the law of conservation of mass and atoms in chemical reactions, the kinds of atoms and mass remain constant (so options with change in kinds of atoms or mass are wrong). Energy can change (but the key is the property and identity change).

Answer:

the properties and identity of the reacting substances