$(a)$ Predict which of the following will form anions and which will form cations:
$(i)$ $Na$ $(ii)$ $Al$ $(iii)$ $Cl$ $(iv)$ $O$
$(b)$ Name two elements that are inert.

Find the atomic number of the element whose electronic configuration is $2, 8, 5$.

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.

Properties of the elements are given below. Where would you locate the following elements in the periodic table?
$(a)$ $A$ soft metal stored under kerosene.
$(b)$ An element with variable (more than one) valency stored under water.
$(c)$ An element which is tetravalent and forms the basis of organic chemistry.

Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
$(a)$ Name the elements which have taken the place of these elements.
$(b)$ Mention the group and the period of these elements in the Modern Periodic Table.

Calcium is an element with atomic number $20$.
$(i)$ Will it be a metal or a non-metal?
$(ii)$ What will be its valency?
$(iii)$ What would be the formula of its chloride?
$(iv)$ Will it be larger or smaller than $K$ (Potassium)?