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.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.

that's what i got you can count the number of atoms