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

Two bodies of masses $0.1\, kg$ and $0.4\, kg$ move towards each other with the velocities $1\, m/s$ and $0.1\, m/s$ respectively. After collision they stick together. In $10\, s$ the combined mass travels ............... $m$.

$A$ solid cylinder of mass $M$ and radius $R$ rolls without slipping down an inclined plane of length $L$ and height $h$. What is the velocity of its center of mass when the cylinder reaches the bottom of the incline?

The diode used in the circuit shown in the figure has a constant voltage drop of $0.5 \, V$ at all currents and a maximum power rating of $100 \, mW$. What should be the value of the resistor $R$,connected in series with the diode,for obtaining maximum current?

Which of the following is an example of a biofertilizer?

The electronic configurations of four elements are given as:
$(I) 1s^2, (II) 1s^2 2s^2 2p^2, (III) 1s^2 2s^2 2p^5, (IV) 1s^2 2s^2 2p^6$. Which configuration has the ability to form both ionic and covalent bonds?