The correct answer is (b).
Section 28 of the Transfer of Property Act, 1882 is based on the doctrine of acceleration. The doctrine of acceleration states that if a debt is payable in installments, and the debtor defaults on one or more installments, the entire debt becomes due immediately.
Section 28 of the Transfer of Property Act, 1882 states that if a mortgagee sells the mortgaged property, the mortgagor is liable to pay the entire mortgage debt immediately. This is because the mortgagee is taking on the risk of not being able to collect the debt in full if the mortgagor defaults on the mortgage payments.
The other options are incorrect because they do not deal with the doctrine of acceleration. Section 27 of the Transfer of Property Act, 1882 deals with the transfer of property by a person who is not the owner. Section 29 of the Transfer of Property Act, 1882 deals with the transfer of property by a person who is the owner but does not have the right to transfer it. Section 30 of the Transfer of Property Act, 1882 deals with the transfer of property by a person who is the owner and has the right to transfer it, but the transfer is void or voidable.