Which one of the following is correct?

$A$ film of water is formed between two straight parallel wires of length $10\,cm$ each,separated by $0.5\,cm$. If their separation is increased by $1\,mm$ while still maintaining their parallelism,how much work will have to be done? (Surface tension of water = $7.2 \times 10^{-2}\,N/m$)

Two identical charged spherical drops, each of capacitance $C$, merge to form a single drop. The resultant capacitance is:

If $A+C=2B$,then $\frac{\cos C-\cos A}{\sin A-\sin C}$ is equal to

From which plant did $D.J. Ivanowsky$ discover viruses?

When a mass $m$ is connected individually to two springs $S_1$ and $S_2$,the oscillation frequencies are $v_1$ and $v_2$. If the same mass is attached to the two springs as shown in the figure,the oscillation frequency would be