Arrange the following elements in the increasing order of their metallic character:
$Mg, Ca, K, Ge, Ga$

State whether the following statement is true or false: In $1913$,Dmitri Ivanovich Mendeleev showed that the atomic number of an element is a more fundamental property than its atomic mass.

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

Why does the basic character decrease along a period? Give reasons.

$(a)$ Why do we classify elements?
$(b)$ What were the two criteria used by Mendeleev in creating his Periodic Table?
$(c)$ Why did Mendeleev leave some gaps in his Periodic Table?
$(d)$ In Mendeleev's Periodic Table,why was there no mention of noble gases like Helium,Neon,and Argon?
$(e)$ Would you place the two isotopes of chlorine,$Cl-35$ and $Cl-37$,in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.

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.