Identify the incorrect statements regarding primary standard of titrimetric analysis.

(A) It should be purely available in dry form.

(B) It should not undergo chemical change in air.

(C) It should be hygroscopic and should react with another chemical instantaneously and stoichiometrically.

(D) It should be readily soluble in water.

(E) $$\mathrm{KMnO}_4$$ & $$\mathrm{NaOH}$$ can be used as primary standard.

Choose the correct answer from the options given below :

What is the structure of C?

The electronic configuration of $$\mathrm{Cu}(\mathrm{II})$$ is $$3 \mathrm{~d}^9$$ whereas that of $$\mathrm{Cu}(\mathrm{I})$$ is $$3 \mathrm{~d}^{10}$$. Which of the following is correct?

In which one of the following pairs the central atoms exhibit $$\mathrm{sp}^2$$ hybridization ?