We know that the magnitude and direction of angular momentum is quantized in quantum mechanics. We can explain the quantization with the help of quantum numbers. But actually who is responsible for this quantization? What is the significance of the reference direction? Can we take any arbitrary direction as the reference axes while considering space quantization? The angular momentum will be oriented in a particular direction (angle) with reference axis, then how other orientations are possible? ( as explained by different magnetic quantum numbers).