Correct Answer  Option 1 : 1.25 × 10
^{3} m/s
The correct answer is option 1) i.e. 1.25 × 103 m/s
CONCEPT:

Drift velocity: The average velocity attained by the electrons under the influence of an electric field is termed the drift velocity.
 The free electrons are always in a constant random motion in the conductor.
 When the conductor is connected to a battery, an electric field is generated.
 When these free electrons are subjected to an electric field, they slowly drift in the direction of the electric field applied, while maintaining the random motion.
 At this point, the net velocity of the electrons is called its drift velocity.
The drift velocity (vd) of the electron in a conductor is given by:
\(v_d =\frac{I}{nAq}\)
Where I is the current flowing through the conductor, A is the area of crosssection of the conductor, q is the charge on the electron and n is the number of electrons.
CALCULATION:
Given that:
Current, I = 20 A
Crosssectional area of conductor, A = 102 cm2 = 10^{6 }m^{2}
Density of electrons in the wire, n = 1029 electrons per m3
\(\Rightarrow v_d= \frac{20}{(10^{29})\;\times\;(10^{6})\;\times\;(1.6\;\times\;10^{19})}=1.25 \times 10^{3}\:m/s\)