The electronic configuration of a metal $M$ is $1s^2 2s^2 2p^6 3s^1$. What will be the formula of its oxide?

What would be the formula of the compound formed between the following elements?
$(i)$ Aluminium and Bromine
$(ii)$ Sodium and Oxygen
$(iii)$ Silicon and Oxygen
$(iv)$ Phosphorus and Chlorine

Consider the elements:
$Cs, Ne, I$ and $F$
$(a)$ Identify the element that exhibits only negative oxidation state.
$(b)$ Identify the element that exhibits only positive oxidation state.
$(c)$ Identify the element that exhibits both positive and negative oxidation states.
$(d)$ Identify the element which exhibits neither the negative nor does the positive oxidation state.

The most common oxidation state of an element is $-2$. The number of electrons present in its outermost shell is

Explain the periodicity of valence or oxidation states and explain the oxidation states of oxygen in $Na_2O$ and $OF_2$.

Arrange the acids $(I)$ $H_2SO_3$,$(II)$ $H_3PO_3$,and $(III)$ $HClO_3$ in the decreasing order of acidity.