Key capacitor fact

For any capacitor, the two plates always carry equal and opposite charges.

So for the $10\,\mu F$ capacitor:

• left plate charge $= -30\,\mu C$
• right plate charge $= +30\,\mu C$

Use the node charge balance

In the given circuit, the right plate of the $10\,\mu F$ capacitor is directly connected to the left plate of the $6\,\mu F$ capacitor by a conducting junction.

Since this junction is isolated, the net charge on that conductor must remain zero.

Therefore, if the right plate of the $10\,\mu F$ capacitor has charge $+30\,\mu C$, then the left plate of the $6\,\mu F$ capacitor must have charge $-30\,\mu C$

Apply equal and opposite charge rule to the $6\,\mu F$ capacitor

For the $6\,\mu F$ capacitor, its two plates must have equal and opposite charges.

Hence if its left plate has charge $-30\,\mu C$, then its right plate must have charge $+30\,\mu C$

Compare with the options

The charge on the right plate of the $6\,\mu F$ capacitor comes out to be $+30\,\mu C$

But this value is not present in the options.

Check consistency with stored answer

The stored correct answer is B: $+18\,\mu C$, but that does not follow from capacitor charge rules for the usual series connection interpretation.

Thus the stored answer appears inconsistent with the given data/options unless the missing figure contains some additional connection not described in the text.