Hope this helps! If in need of clarification, feel free to ask :)
D. is the correct answer.
Current at all points of a series circuit must be the same, because there's no place in the circuit where electrons are being manufactured, and no place where they're leaking out and falling on the floor. The nimber of electrons that leaves the loop is the same number that entered it.
I'm not sure what is nmeant by "p.d. remains different" .
Answer:
12 cm
Explanation:
We shall use Lens makers formula here which is as follows

Put μ = 1.5 , R₁ = 10 cm ,R₂ = - 15 cm ( according to sign convention )

= .5 x ( 15 + 10 ) / 15 x 10
= 
F = 12 cm
Answer:
Let the power delivered by the sound wave be 'P'
Intensity by definition is the power delivered per unit area.
i.e. I =
dA
dP
;
In spherical polar coordinate system dA = r
2
Ω
I =
r
2
Ω
dP
;
I ∝
r
2
1
So if distance increases 3 fold. The Intensity becomes
9
1
times the initial