Question

though chlorenchyma ,arenchyma and storage tissue are parenchyma in nature .why do they have different names?

Answer 1

It's because they have different functions. 
Chlorenchyma: It's is filled with chlorophyll and helps in photosynthesis.
Aerenchyma: It's filled with air and are present especially in aquatic plants and helps them to float.
Parenchyma in the form of storage sacs help in storage and give support by filling the empty spaces.

Answer 2

Answer:

Chlorenchyma, Aerenchyma and storage tissue are parenchyma

These three parenchymatous tissues are modified to perform various functions. parenchymatous tissues.

The parenchyma which contains chloroplasts is called chlorenchyma. It performs photosynthesis.

The parenchyma which contains large air cavities or spaces is called Aerenchyma. It helps the plant to float.

The parenchyma which stores water or food or waste products is called storage tissue.