Question

1. choose all that apply.

which two of these are required for a compound to be formed by elements?
must physically combine
must chemically combine
must be in reciprocal proportions
must be in definite proportions

Explanation:

A compound is formed when elements chemically combine. Also, the elements in a compound are present in definite proportions. Physical combination forms a mixture, not a compound. Reciprocal proportions is not a requirement for compound formation.

Answer:

must chemically combine, must be in definite proportions