Which of the following statements is not correct regarding the trends observed when moving from left to right across the periods of the Periodic Table?

Which of the given elements $A, B, C, D$ and $E$ with atomic numbers $2, 3, 7, 10$ and $30$ respectively belong to the same period?

An element belongs to the third period and second group of the periodic table:
$(a)$ State the number of valence electrons in it.
$(b)$ Is it a metal or a non-metal?
$(c)$ Name the element.
$(d)$ Write the formula of its oxide.

An element $X$ belongs to the $3rd$ period and group $16$ of the Modern Periodic Table.
$(a)$ Determine the number of valence electrons and the valency of $X$.
$(b)$ Write the molecular formula of the compound formed when $X$ reacts with hydrogen and draw its electron dot structure.
$(c)$ Name the element $X$ and state whether it is metallic or non-metallic.

Why does atomic size decrease as we move from left to right along a period in the periodic table?

The atomic number of an element is $17$. Predict $(a)$ its valency,$(b)$ whether it is a metal or non-metal,$(c)$ its relative size with respect to other members of its group. Justify your answer in each case.