$(a)$ How does electropositivity of elements get affected as we move :
$(i)$ down a group
$(ii)$ across a period?
$(b)$ Which atomic property increases both as we move across a period or down a group?

$Li, Be, B$ and $C$ are the elements of the same period of the Modern Periodic Table.
$(a)$ Arrange them in increasing order of their atomic size.
$(b)$ In which shell (number) would the last electron enter for all of them?
$(c)$ Calculate the number of valence electrons in each.
$(d)$ Which element amongst them is most electropositive?

Which of the following statement$(s)$ about the Modern Periodic Table are incorrect?
$(i)$ The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number.
$(ii)$ The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses.
$(iii)$ Isotopes are placed in adjoining group$(s)$ in the Periodic Table.
$(iv)$ The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.

Which of the following is the outermost shell for elements of period $2$?

An element $X$ (atomic number $17$) reacts with an element $Y$ (atomic number $20$) to form a divalent halide.
$(a)$ What will be the nature of oxide of element $Y$? Identify the nature of bonding in the compound formed.
$(b)$ Draw the electron dot structure of the divalent halide.

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.