Question

what does the period number indicate in an element’s electron cloud?
number of protons
number of valence electrons
atomic mass
number of energy levels

Explanation:

To determine the correct answer, we analyze each option:

• "Number of protons" is determined by the atomic number, not the period number.
• "Number of valence electrons" is related to the group number, not the period number.
• "Atomic mass" is the sum of protons and neutrons, unrelated to the period number.
• "Number of energy levels" (shells) in an element's electron cloud is indicated by the period number. For example, elements in period 1 have 1 energy level, period 2 have 2, etc.

Answer:

D. Number of energy levels (assuming the options are labeled A to D as: A. Number of protons, B. Number of valence electrons, C. Atomic mass, D. Number of energy levels)