It was found that the law of octaves was applicable only up to:

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.

Why does atomic size decrease as we move from left to right along a period in the periodic table?

What would be the nature of oxides formed by the elements on the right-hand side of the periodic table?

$(a)$ Identify the element that has two completely filled shells and the number of valence electrons in each are as: $(i)$ $1$,$(ii)$ $2$,$(iii)$ $7$,$(iv)$ $8$. $(b)$ Analyse which amongst them is inert.

List any two properties of the elements belonging to the first group of the modern periodic table.