Which of the following is true about rows of the periodic table?
atomic mass increases from left to right.
the chemical properties of the elements will be similar
the number of protons decreases as you go from left to right
atomic number increases from right to left.

The right answer is the first one: Atomic mass increases from left to right.

Explanation:

The main characteristic of the rows in the periodic table is that the mass increases from left to right and that is because every atom gains an electron an a proton from one position to the next one in a row.

The second one is incorrect, in a row the atoms don't have similar chemical properties.

The third one is also incorrect because the number of protons increases from left to right.

And also the atomic number increases from left to right.