What is the difference between 802.11b and 802.11g? and what type of frequency used?
802.11b uses 2.4GHz as does 802.11g. The difference between them is the way in which the data is encoded onto the carrier:
802.11b uses DSSS (Direct Sequence Spread Spectrum) which has loads off issues, mainly bandwidth and multi-path.
802.11g uses OFDM (Orthogonal Frequency Divisional Multiplex) for higher modular rates from BPSK up-to 64QAM. However it also uses CCK (Complementary Code Keying) this is for backward compatibility with 802.11b.