Which of the following statements about the periodic table is correct?

Step-by-step reasoning:

• Elements in the same period have the same number of valence electrons → False. They have the same number of electron shells, not valence electrons.
• Elements in the same group have the same number of electron shells → False. Elements in the same group have the same number of valence electrons, not shells.
• The non-metallic properties of the elements tend to decrease across each period → False. Non-metallic character actually increases across a period from left to right.
• The number of valence electrons increases progressively across a period → True. As you go from left to right in a period, each successive element has one more valence electron.

Final Answer: The number of valence electrons increases progressively across a period