Vulcanization of rubber was discovered by: MCQ with Answer and Explanation

Explanation:
Azotobacter is a free-living aerobic bacterium that fixes atmospheric nitrogen in the soil, making it available to non-leguminous crops. Rhizobium is symbiotic and specific to legumes. Nitrobacter and Nitrosomonas are involved in nitrification (converting ammonia to nitrites/nitrates), not nitrogen fixation.

Explanation:
The element with atomic number 17 is Chlorine. Its electronic configuration is 2, 8, 7. It has 3 shells, so it is in Period 3. It has 7 valence electrons, so it belongs to Group 17 (10 + 7 = 17 in modern IUPAC notation) along with fluorine, bromine, and iodine.

Explanation:
Methyl orange is red at pH < 3.1 and yellow at pH > 4.4. Litmus: red in acid, blue in base. Phenolphthalein: colorless in acid, pink in base. Turmeric: yellow in acid, reddish-brown in base.