Is a deed of mortgage possible on immoveable plot that is not partitioned?

A single person cannot mortgage the entire undivided property. 

If all the owners jointly execute a mortgage deed then the property can accepted towards mortgage loan. 

No, joint property can  be mortgaged only when all owners of property jointly execute mortgage deed .

Sorry but I forgot some details. The plot has two parts. The plot was purchased jointly by my mother and her sister. Then they partitioned it among themselves informally but never filed the partition before the authorities. Later I and my brother bought from my mother's sister her part of 2 acres.

We got our part mutated. My mother did not get her part mutated.   

Now the official ownership land record shows one survey number for both plots with three names: My mother and two brothers (myself and my brother). My question is: Can we  two brothers do a deed of mortgage on our part of the plot even though it is not partitioned?  Remember that the two plots still have only one survey number.

Thank you so much.

If you have a registered sale deed on you and your brotehr's name to the property that you would like to submit as collateral security, then there is no question of partition at all besides there is a joint patta in which both your names are found available.

It requires only a formal partition between your mother and you both.

Thank you but before the formal partition, can brothers mortgage their part of the land alone?

The formal partition can happen anytime after that also becasue it is just dividing both the properties in the revenue records and not physically because the properties have already been physically partitioned.

If the bank accepts and recognises your title to the property offered as collateral security in the mortgage loan, you can very well proceed.