Which one of the following elements reacts with steam?

On addition of $1 \, mL$ solution of $10\% \, NaCl$ to $10 \, mL$ gold sol in the presence of $0.0250 \, g$ of starch,the coagulation is just prevented. What is the gold number of starch?

The $rms$ value of the electric field of light coming from the Sun is $720\, N/C$. The average total energy density of the electromagnetic wave is

Bond dissociation energies of $HF$,$HCl$,and $HBr$ follow the order:

If the slopes of the lines given by the equation $ax^2+2hxy+by^2=0$ are in the ratio $5:3$,then the ratio $h^2:ab$ is:

$A$ vertical spring with force constant $K$ is fixed on a table. $A$ ball of mass $m$ at a height $h$ above the free upper end of the spring falls vertically on the spring so that the spring is compressed by a distance $d$. The net work done in the process is