Q.Since the input impedance of an ideal operational amplifier is infinite :

Infinite input impedance directly forces the input current of an ideal op-amp to be zero — this is one of the two 'golden rules' used to analyse ideal op-amp circuits.

An operational amplifier is modelled, in the ideal limit, with two defining properties at its input: infinite input impedance and infinite open-loop gain (together with, usually, zero output impedance). Input impedance $Z_{in}$ is the ratio of the voltage applied between (or at) the input terminals to the current drawn by those terminals: $Z_{in} = V_{in}/I_{in}$. If $Z_{in}\to\infty$, then for any finite input voltage $V_{in}$, the input current $I_{in} = V_{in}/Z_{in} \to 0$. This is exactly the first of the two idealised 'golden rules' of op-amp analysis (the second being that the differential input voltage is driven to zero under negative feedback, i.e. a 'virtual short').

Physically, this reflects the fact that a real op-amp's input stage is a differential amplifier built from transistors (BJT or, more commonly today, FET) whose input terminals draw only a tiny bias/leakage current in practice; treating this as exactly zero is the standard, extremely good approximation used throughout circuit analysis.

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