1 Which of the following is a chemical reaction?
А
Sodium and chlorine atoms bond to form salt molecules
B.
Ice melts to form water
С
Carbon dioxide freezes to form dry ice
D
Salt and water mix to form salt water

a because two substances form a new substance

Explanation:

A is the chemical reaction because  we can see rearrangement of the ionic structure of a substance, new bonds are forming up that results in the change in physical and chemical properties

"hydrogen bonding is the attraction of h atoms in the water molecule (slight + charge) to o atoms in a neighboring water molecule (slight - charge); it is a weak interatomic force. but it is still strong enough to the water molecules "stick" together."

it's c. elements are placed in rows based on how may valencies electrons have.