An op-amp is said to be ideal if it has the following characteristics.
Open loop voltage gain (AOL) is infinity.
Input resistance (Ri) is infinity.
Output resistance (Ro) is zero.
Bandwidth (BW) is infinity.
Zero off-set (i.e) V0 = 0, when V1 = 0 & V2 = 0.
An ideal op-amp cross no current and both the input terminal i 1 = i2 = 0. Because gain is infinite the voltage between inverting and non-inverting terminals i.e op-amp is essentially zero for infinite output voltage V0 is independent of the current drawn from the output is R0 = 0.