The experiment of transforming principle was conducted on:

The correct answer is Option (1) → Streptococcus pneumoniae

The transforming principle was Griffith’s name for the unknown substance that changed one kind of bacterium into another. He worked with two strains of Streptococcus pneumoniae: the S strain (smooth, with a mucous coat, which kills mice) and the R strain (rough, harmless). Heat-killed S cells mixed with live R cells killed the mice, because some R cells had been transformed into S cells.

Option (1) Streptococcus pneumoniae — Correct. This pneumonia-causing bacterium was used in all of Griffith’s experiments.

Option (2) Rhino virus — Incorrect. Rhino viruses cause the common cold. They were not used in the transformation experiments.

Option (3) Plasmodium vivax — Incorrect. It is the protozoan that causes malaria.

Option (4) Salmonella typhi — Incorrect. It is the bacterium that causes typhoid.

NCERT Extract:
The Search for Genetic Material – “… Transforming Principle In 1928, Frederick Griffith, in a series of experiments with Streptococcus pneumoniae (bacterium responsible for pneumonia), witnessed a miraculous transformation in the bacteria. During the course of his experiment, a living organism (bacteria) had changed in physical form.”