The correct option is 1 and 2 only.

Brahmo Samaj was a socio-religious reform movement founded by Raja Ram Mohan Roy in 1828. The main objectives of the movement were to reform Hindu society and to promote monotheism and moral values.

The key beliefs of Brahmo Samaj were:

1. Rejection of idol worship: Brahmo Samaj rejected the traditional Hindu practice of idol worship, as it believed in the worship of an abstract God.

2. Denial of the need for a priestly class: Brahmo Samaj believed that there was no need for a priestly class for interpreting religious texts as all individuals could interpret them themselves.

3. Denial of the infallibility of the Vedas: Brahmo Samaj did not popularize the doctrine that the Vedas are infallible. In fact, it rejected many of the superstitions and beliefs associated with the Vedas and emphasized the need for rational and scientific inquiry.

Therefore, option (b) "1 and 2 only" is the correct answer.