Which of the following is the strongest reducing agent?

In land plants,the guard cells differ from other epidermal cells in having:

For the reaction $C_{(s)} + CO_{2_{(g)}} \rightleftharpoons 2CO_{(g)}$,the partial pressures of $CO_2$ and $CO$ are $2.0 \ atm$ and $4.0 \ atm$ respectively at equilibrium. The $K_p$ for the reaction is

The metal used for the de-bromination reaction of $1, 2-dibromoethane$ is:

$A$ bar of cross-sectional area $A$ is subjected to two equal and opposite tensile forces at its ends as shown in the figure. Consider a plane $BB'$ making an angle $\theta$ with the length. The ratio of tensile stress to the shearing stress on the plane $BB'$ is