Which of the following absorbs oxygen rapidly?

The first and second dissociation constants of a diprotic acid $H_2A$ are $1.0 \times 10^{-5}$ and $5.0 \times 10^{-10}$ respectively. The overall dissociation constant of the acid is:

In which of the following acid-base titrations is the $pH$ at the equivalence point greater than $8$?

Blue litmus turns red in the following mixture of acid and base:

What would happen when a solution of potassium chromate is treated with an excess of dilute nitric acid?

The $pK_{b}$ of dimethylamine and $pK_{a}$ of acetic acid are $3.27$ and $4.77$ respectively at $T(K)$. The correct option for the $pH$ of dimethylammonium acetate solution is :