Using 1 Bit we can represent 2^1 i.e 2 memory locations. 
Using 2 bits, we can represent 2^2 i.e. 4 memory locations. 
Using 3 bits, we can represent 2^3 i.e. 8 memory locations. 
Therefore, if we generalize this, 
Using n bits, we can assign 2^n memory locations.  

n bits of address  → 2 ^ n memory locations