When Mendeleev started his work,the number of known elements were:

Which of the following is the outermost shell for elements of period $2$?

The atomic radii of the elements of the second period are given below:

Second period elements	$B$	$Be$	$O$	$N$	$Li$	$F$	$C$
Atomic Radii $(pm)$	$88$	$111$	$66$	$74$	$152$	$64$	$77$

$(i)$ Arrange these elements in decreasing order of their atomic radii.
$(ii)$ Are the elements now arranged in the pattern of a period in the periodic table?
$(iii)$ Name the element which has the $(a)$ smallest and $(b)$ largest atomic number.
$(iv)$ From the above data, infer how the atomic size or atomic radius of the elements changes as we move from left to right in a period.
$(v)$ Name one metal, one non-metal, and a metalloid out of these elements.
$(vi)$ Why does atomic radius decrease as we move from left to right in a period?

Which one of the following does not increase while moving down the group of the periodic table?

Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at Periodic Law?

Arrange the following elements in the order of their increasing nonmetallic character:
$Li, O, C, Be, F$