The correct option is (C) 8.4 × 105.
Explanation:
Optical source frequency = f (c/λ) = [(3 × 108) / (800 × 10–9)] = 3.8 × 1014Hz
BW of channel = 1% of f
∴ BW of channel = 3.8 × 1012Hz
No. of channels = [(Total BW of channel) / (BW needed per channel)]
= [(3.8 × 1014) / (4.5 × 106)]
∴ No. of channels = 8.4 × 105