Microbe responsible for converting milk to curd is:

The correct answer is Option (2) → Lactobacillus

Option (1) Saccharomyces cerevisiae — Incorrect. Yeast is used for bread and alcohol.

Option (2) Lactobacillus — Correct. Lactic acid bacteria turn milk into curd.

Option (3) E. coli — Incorrect. E. coli is a gut bacterium used in genetic engineering.

Option (4) Lens culinaris — Incorrect. Lens culinaris is the lentil plant, not a microbe.

NCERT Extract:
Microbes in Household Products – “… You would be surprised to know that we use microbes or products derived from them everyday. A common example is the production of curd from milk. Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B12.”