The minimum number of 2-input NOR gates required to implement a 2-input AND gate is:

Explanation

To implement a 2-input AND gate using only NOR gates (universal logic): step 1 invert A using NOR (A’), step 2 invert B using NOR (B’), step 3 pass A’ and B’ into a third NOR gate ((A’ + B’)’ = A * B). Hence, 3 NOR gates are required.