Consider statements about human diseases: 1. Typhoid is caused by Salmonella typhi. 2. Malaria is caused by a virus. 3. Ringworm is a fungal infection. Which are correct? MCQ with Answer and Explanation

Explanation:
Intrinsic factor, a glycoprotein secreted by gastric parietal cells, binds to vitamin B₁₂ and facilitates its absorption in the ileum. Absence or deficiency (pernicious anemia) leads to B₁₂ deficiency, causing megaloblastic anemia and neurological symptoms. HCl activates pepsin, pepsinogen is precursor, mucus protects.

Explanation:
Folic acid (vitamin B₉) is reduced to tetrahydrofolate (THF), which carries one-carbon groups in amino acid and nucleotide metabolism. Biotin is for carboxylation, riboflavin for redox, thiamine for decarboxylation.

Explanation:
Acid rain, containing sulfuric and nitric acids, corrodes buildings, monuments (like the Taj Mahal), and statues made of limestone and marble. The depletion of the stratospheric ozone layer reduces its ability to absorb harmful ultraviolet (UV-B) radiation, increasing the amount reaching the Earth's surface. Global warming is caused by an increase, not a decrease, in atmospheric greenhouse gases (like CO2 and methane), which trap more heat. Thus, statements 1 and 2 are correct.