During the borax bead test with $$\mathrm{CuSO_4}$$, a blue green colour of the bead was observed in oxidising flame due to the formation of :

"A" obtained by Ostwald's method involving air oxidation of NH$$_3$$, upon further air oxidation produces "B", "B" on hydration forms an oxoacid of Nitrogen along with evolution of "A". The oxoacid also produces "A" and gives positive brown ring test.

Identify A and B, respectively :

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R

Assertion A : Carbon forms two important oxides - CO and CO$$_2$$. CO is neutral whereas CO$$_2$$ is acidic in nature

Reason R : CO$$_2$$ can combine with water in a limited way to form carbonic acid, while CO is sparingly soluble in water

In the light of the above statements, choose the most appropriate answer from the options given below :