The electric field intensity in air at a point $20\; cm$ from a point charge $Q$ coulombs is $4.5 \times 10^5\;N/C$. The magnitude of $Q$ is :

Question

( A ) $1 \; \mu C$
( B ) $0.2 \; \mu C$
( C ) $0.1\; \mu C$
( D ) $2 \; \mu C$