Which from following statements regarding mercury battery is NOT true?

The molar conductivity of $0.04$ M $\text{AB}_2$ type salt solution at $300$ K is $200\,\Omega^{-1}\text{cm}^2\text{mol}^{-1}$. Find the conductivity.

The time required for $90\%$ completion of a certain first order reaction is $1$ hour. Calculate the time required for $99.9\%$ completion of the same reaction.

The rate of the reaction $2A + 3B \rightarrow 2C + D$ is $6 \times 10^{-4} \text{ mol dm}^{-3}\text{ s}^{-1}$, when $[A] = [B] = 0.3 \text{ mol dm}^{-3}$. If the reaction is of first order for A and zeroth order for B, then find the rate constant.