A conducting sphere is charged. If the electric field at a distance 20 cm from the centre of the sphere is $1.2 \times 10^3 NC^{-1}$ and points radially inwards, the net charge on the sphere is:

$4.5 \times 10^9 C$ $-4.5 \times 10^{-9} C$ $1.7 \times 10^9 C$ $-5.3 \times 10^{-9} C$

$-5.3 \times 10^{-9} C$

The correct answer is Option (4) → $-5.3 \times 10^{-9} C$