A ball of mass 10 g is moving with a velocity of 50 m −1 . On applying a constant force on ball for 2.0 s, it acquires a velocity of 70 m −1 . Calculate : (i) the initial momentum of ball, (ii) the final momentum of ball, (iii) the rate of change of momentum, (iv) the acceleration of ball, and

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current

Sound wavelength of visible light waves

Chope i i hope i did