What type of oxide would Eka-aluminium form?

Three elements $X$,$Y$,and $Z$ have atomic numbers $7$,$8$,and $9$ respectively.
$(a)$ State their positions (Group number and period number both) in the Modern Periodic Table.
$(b)$ Arrange these elements in the decreasing order of their atomic radii.
$(c)$ Write the formula of the compound formed when $X$ combines with $Z$.

What type of oxide would Eka-aluminium form?

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.

What is meant by 'group' in the modern periodic table? How do the following change on moving from top to bottom in a group?
$(i)$ Number of valence electrons
$(ii)$ Number of occupied shells
$(iii)$ Size of atoms
$(iv)$ Metallic character of elements
$(v)$ Effective nuclear charge experienced by valence electrons.

The order of increasing atomic size is: