Q1: All the voltage drops and the source voltage added together in a series circuit is equal to

ANS:C - zero

If we have given some value of voltage in a series ckt so exactly voltage drop due to series ckt that's why the sum of all the voltage drops equals to the source voltage.

Vs = Vd, or Vs - Vd = 0.

For example; we have given 5V as the source voltage and we have two resistors one drop 2V and the other drop 3V, then first we add drop voltage, which is equal to Vd= 2V+3V= 5V.

Now simply we know that Vs = Vd therefore,
5V = 5V or 5V-5V=0, 0volts.