What were the limitations of Dobereiner’s classification ?

Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.

Name

$(a)$ three elements that have a single electron in their outermost shells.

$(b)$ two elements that have two electrons in their outermost shells.

$(c)$ three elements with filled outermost shells.

The position of three elements $A$, $B$ and $C$ in the Periodic Table are shown below

$ (a)$ State whether $A$ is a metal or non-metal.

$(b)$ State whether $C$ is more reactive or less reactive than $A$.

Why do you think the noble gases are placed in a separate group ?

Which element has

$(a)$ a total of three shells, with four electrons in its valence shell?

$(b)$ a total of two shells, with three electrons in its valence shell?

$(c)$ twice as many electrons in its second shell as in its first shell?