Whats the effect? A wave enters a new medium perpendicular to the boundary between the two media.

A wave

Explanation:

Because it’s the one that’s cause the new medium to go between the two media.

answer: -

reaction:

na + cl ⇌ nacl

balanced chemical equation:

na + 2cl ⇌ nacl2

sodium + clorine goes to form sodium chloride (table salt).

the product is nacl2.

and the reactants are na and cl.

(note: if you don’t know what ⇌ means, read below: -

⇌(double head arrow) means reversible reaction).