Typhoid is caused by -

The correct answer is Option (1) → Salmonella typhi

Option (1) Salmonella typhi — Correct. Salmonella typhi causes typhoid.

NCERT Extract:
Common Diseases in Humans – “… Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings. These pathogens generally enter the small intestine through food and water contaminated with them and migrate to other organs through blood. Sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache and loss of appetite are some of the common symptoms of this disease. Intestinal perforation and death may occur in severe cases. Typhoid fever could be confirmed by Widal test : A classic case in medicine, that of Mary Mallon nicknamed Typhoid Mary, is worth mentioning here.”