How do elements change as you move to the right along a row in the periodic table?

The atomic number decreases.

The electronegativity decreases.

The average atomic mass increases.

The number of valence electrons decreases.

The answer to your question is The average atomic mass increases

Explanation:

As we move to the right along the periodic table, the atomic number of the elements increases, the electronegativity also increases the average atomic mass increases and the number of valence electrons increases. So the right answer is the third option.

The average atomic mass increases.

Explanation:

The atomic number ( = the number of protons) increases by 1 as you move to the right.

The electronegativity increases.

The number of valency electrons increases.