The electronic configurations of $4$ elements $A, B, C,$ and $D$ are as follows:
$A: 2, 1$
$B: 2, 2$
$C: 2, 8, 2$
$D: 2$
$(a)$ Which of these elements belong to the same group? Name them.
$(b)$ Which of these elements belong to the same period? Name them.
$(c)$ Which of these elements is inert? Name it.

Complete the following crossword puzzle (Figure):
**Across:**
$(1)$ An element with atomic number $12$.
$(3)$ Metal used in making cans and member of Group $14$.
$(4)$ $A$ lustrous non-metal which has $7$ electrons in its outermost shell.
**Down:**
$(2)$ Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene.
$(5)$ The first element of second Period.
$(6)$ An element which is used in making fluorescent bulbs and is second member of Group $18$ in the Modern Periodic Table.
$(7)$ $A$ radioactive element which is the last member of halogen family.
$(8)$ Metal which is an important constituent of steel and forms rust when exposed to moist air.
$(9)$ The first metalloid in Modern Periodic Table whose fibres are used in making bullet-proof vests.

The position of some elements $A, B, C, D, E, F$ and $G$ in the Modern Periodic Table is given as under:

Group $\to$	$16$	$17$	$18$
Period $1$			$A$
Period $2$	$B$	$C$	$D$
Period $3$	$E$	$F$	$G$

$(a)$ In which group are inert elements placed?
$(b)$ What type of ions would $B, C, E,$ and $F$ form?
$(c)$ Which element would have chemical properties similar to $C$?
$(d)$ How many shells would $A$ have?
$(e)$ What is the similarity between $A$ and $D$?
$(f)$ Identify the most abundant element in the earth's crust.

Compare and contrast the arrangement of elements in Mendeleev's Periodic Table and the Modern Periodic Table.

An element is placed in $2^{nd}$ Group and $3^{rd}$ Period of the Periodic Table. It burns in the presence of oxygen to form a basic oxide.
$(a)$ Write a balanced chemical equation when this oxide is dissolved in water.
$(b)$ Draw the electron dot structure for the formation of this oxide.

Given below are four elements with their atomic numbers:

Element	Atomic Number
$A$	$16$
$B$	$11$
$C$	$3$
$D$	$14$

$(a)$ Identify the elements which belong to the same group of the Modern Periodic Table.
$(b)$ Arrange the given elements in decreasing order of atomic size.
$(c)$ Write the formula of the oxide of $B$.
$(d)$ Which of the above elements is a metalloid?