State as to why
(a) Alkali metals show only +1 oxidation state. (b) Na and K impart colour to the flame but Mg does not.(c) Lithium on being heated in air mainly forms the monoxide and not the peroxide.(d) Li is the best reducing agent in aqueous solution.

a) There is only one valence electron in Alkali metals, on loosing one electron alkali metals achieve noble gas configuration which is most stable. Therefore, in order to achieve stability Alkali metals show only +1 Oxidation state.

b) Na and K impart colour to the flame due to low ionisation energy. So, the loosely bound electron get excited when exposed to light. Due to the small size of Mg the electrons are bound to the nucleus tightly. So a large amount of energy is required for this process.

c) Due to the small size of Lithium it forms only monoxide. The stability of peroxide and superoxide increases with the increase in the size of metals.

d) Alkali metals have low ionisation energy so are the good reducing agents. Though Li has highest ionisation energy, it is the best reducing as it has high amount of hydration energy which exceeds it's ionisation energy.

a) alkali metals have only 1 electron in their last valence shell so thats why they show +1 oxidation state by attaining the noble gas configuration.

b) if the electrons are single in the last shell they possess very high energy so as the metal gets heated up they excite to the higher energy level by attaining some energy and when they re-emit the absorbed energy the color is imparted.

c) Li⁺ is very small in size. and its in general that a smaller anion is stablized by smaller cation. so being oxide O^2- and peroxide 0₂^2- the smaller and the larger anion respectively. therefore Li⁺ will form oxide not superoxide.

d) reducing agents are those which reduces others but oxidise themselves. oxidation is loosing of electron so because Li readily forms Li⁺ on loosing one electron thus is a reducing agent.