Which element is not present in Nessler's reagent?

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : $$\alpha$$-halocarboxylic acid on reaction with dil. $$\mathrm{NH_3}$$ gives good yield of $$\alpha$$-amino carboxylic acid whereas the yield of amines is very low when prepared from alkyl halides.

Reason (R) : Amino acids exist in zwitter ion form in aqueous medium.

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

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : Gypsum is used for making fireproof wall boards.

Reason (R) : Gypsum is unstable at high temperatures.

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

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : $$\mathrm{Cu^{2+}}$$ in water is more stable than $$\mathrm{Cu^{+}}$$.

Reason (R) : Enthalpy of hydration for $$\mathrm{Cu^{2+}}$$ is much less than that of $$\mathrm{Cu^{+}}$$.

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