Why Open Op-amp is unsuitable for many linear application?

Question:

Why Open Op-amp can not be used for amplification application? 

Answer: 

The open-loop gain of the op-amp is very high. ( Approx 2 lakh)

Only the smaller signal (in order of microvolts or less) having very low frequency maybe amplified accurately without distortion. 

However, signals this small are very susceptible to noise and are almost impossible to obtain in the laboratory. 

Besides being a large gain, it is also not constant. The voltage gain varies with change in temperature and power supply as well as mass production techniques. The variation in the voltage gain is relatively large in the open-loop op-amp in particular, which make the open-loop op-amp unsuitable for the many linear application.