Initial charges: Q1=1 µF×1200V=1200 µC, Q2=2 µF×1200V=2400 µC. Connecting unlike terminals leaves net 2400−1200=1200 µC on combined C=3 µF so V'=400 V; final charges 1 µF×400=400 µC and 2 µF×400=800 µC.

Three in series give C/3, in parallel with C gives total C + C/3 = 4C/3.

With the capacitor isolated the charge remains constant while capacitance decreases as plates separate, so V = Q/C increases.

With the battery disconnected charge remains constant; inserting dielectric increases capacitance, so V decreases and stored energy (½CV²) decreases.

The block's explanatory answer explicitly states A; bringing like (positive) charges closer requires work, increasing their potential energy.

A CRO can display waveforms, measure time intervals between events, and be used as a voltmeter for rapidly changing signals, so all options apply.

The electroscope reading decreases if the effective capacitance to ground increases (i) or if the battery potential is decreased (iv); the block indicates option C.

A falling drop reaches terminal velocity when gravitational and viscous forces balance, so it falls thereafter with a constant velocity.

The OCR shows a 'Y' marker adjacent to option C 'Semiconductors', and semiconductors are indeed the key material behind modern electronics.

Initial charge Q = C1·V1 = 2 μF·200 V = 400 μC; final common V = 20 V so total C = Q/V = 400/20 = 20 μF, hence C2 = 20 − 2 = 18 μF.