The 802.11g standard outlines two mandatory modes along with one optional mode.  Describe each mode.

What will be an ideal response?

The first mandatory mode is the same CCK (complementary code keying) mode used by 802.11b at 11 and 5.5 Mbps. The second mandatory mode for 54 Mbps transmissions uses OFDM like the 802.11a standard but still in the 2.4 GHz frequency. The optional mode can transmit at 22 Mbps and is known as PBCC-22 (Packet Binary Convolution Coding), which can actually transmit between 6 and 54 Mbps.