Which among the following is the conjugate base of $HClO_4$?

Urea is preferred to ammonium sulphate as a nitrogenous fertilizer because

Explain the statement: "$NH_3$ acts as both a Lewis base and a Brønsted-Lowry base,whereas $BF_3$ acts only as a Lewis acid but not as a Brønsted-Lowry acid."

Derive the equation of the relation between the weak base ionization constant $K_b$ and its conjugate acid ionization constant $K_a$.

Which of the following is a conjugate acid-base pair?

The values of dissociation constants $(K_a)$ of some acids (at $25\,^{\circ}C$) are as follows. Indicate which is the strongest acid in water:
$(A)$ $1.4 \times 10^{-2}$
$(B)$ $1.6 \times 10^{-4}$
$(C)$ $4.4 \times 10^{-10}$
$(D)$ $4.3 \times 10^{-7}$