The arrangement of the elements from left to
right in period 4 on the periodic table is based on
(1) atomic mass
(2) atomic number
(3) the number of electron shells
(4) the number of oxidation states

Option (2) is the correct answer.

Explanation:

Elements in a periodic table are placed according to increasing atomic number when we move from left to right.

Atomic mass is the sum of total number of protons and neutrons present in an atom. Whereas atomic number is the sum of only total number of protons present in an atom.

Elements of period 4 are K, Ca, Sc, Ti, V, Cr, Mn, Fe etc. Atomic mass of these elements increases when we move from left to right.

Therefore, we can conclude that the arrangement of the elements from left to  right in Period 4 on the Periodic Table is based on atomic number.

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