$(a)$ State Modern Periodic Law.
$(b)$ Elements $A, B, C$ and $D$ have atomic numbers $1, 8, 11$ and $19$ respectively. Choose the odd element and give reason for your answer.

The element with atomic number $18$ belongs to which group?

Atomic numbers of a few elements are given below: $10, 20, 7, 14$.
$(a)$ What would be the electronic configuration for each of these elements?
$(b)$ Determine the valency of these elements.

Predict the maximum number of valence electrons possible for atoms in the first period of the periodic table.

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

The atomic radii of the elements of the second period are given below:

Second period elements	$B$	$Be$	$O$	$N$	$Li$	$F$	$C$
Atomic Radii $(pm)$	$88$	$111$	$66$	$74$	$152$	$64$	$77$

$(i)$ Arrange these elements in decreasing order of their atomic radii.
$(ii)$ Are the elements now arranged in the pattern of a period in the periodic table?
$(iii)$ Name the element which has the $(a)$ smallest and $(b)$ largest atomic number.
$(iv)$ From the above data, infer how the atomic size or atomic radius of the elements changes as we move from left to right in a period.
$(v)$ Name one metal, one non-metal, and a metalloid out of these elements.
$(vi)$ Why does atomic radius decrease as we move from left to right in a period?