Question

1. in order for elements to form a compound, which two things must happen? must chemically combine must physically combine must be in definite proportions must be in reciprocal proportions 9. choose all that apply. which three descriptions are properties of water? water is nonpolar. water boils at 0 °c. water is clear. water is polar. water has poor thermal conductivity.

Explanation:

For elements to form a compound, they undergo a chemical change and combine in definite proportions. Water is a polar molecule, boils at 100°C under standard - conditions, is clear, and has relatively poor thermal conductivity.

Answer:

For the first question:
must chemically combine, must be in definite proportions
For the second question:
Water is clear, Water is polar, Water has poor thermal conductivity