The element with atomic number $14$ is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?

On moving from left to right in a period in the periodic table,the size of the atom.

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.

$(a)$ 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.

State the reason for the following:
$(a)$ The elements of the same group have similar chemical properties.
$(b)$ The elements of the same period have different properties.

The elements $Be$,$Mg$,and $Ca$,each having two electrons in their outermost shells,are in periods $2$,$3$,and $4$ respectively of the modern periodic table. Answer the following questions,giving justification in each case:
$(i)$ Write the group to which these elements belong.
$(ii)$ Name the least reactive element.
$(iii)$ Name the element having the largest atomic radius.