Hi,
Sorry, there is a mistake in my previous response. Out of the 8 bits for addressing, one bit decides whether the i2c transfer is read or write. So it is 2^7 = 128 slaves theoretically. (I have edited my previous response from 256 to 128 to avoid confusion) But you cannot connect 128 slaves at a time practically because the load will be too much. So if you have appropriate circuitry, it is possible to connect 128 slaves.
