In which one of the following situations a chemical reaction does not occur?

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Q: 78 (NDA-II/2008)
In which one of the following situations a chemical reaction does not occur?

question_subject: 

Science

question_exam: 

NDA-II

stats: 

0,20,16,20,7,7,2

keywords: 

{'chemical reaction': [0, 0, 2, 0], 'coal': [0, 1, 2, 0], 'situations': [0, 0, 1, 0], 'sodium': [10, 2, 12, 23], 'common salt': [0, 0, 0, 1], 'air': [1, 0, 0, 0], 'water': [65, 15, 80, 129], 'moist air': [1, 0, 1, 1], 'iron': [0, 0, 1, 1]}

In option 1, common salt is exposed to air. This situation does not result in a chemical reaction. Common salt, also known as sodium chloride (NaCl), is a stable compound and does not react with oxygen or moisture in the air. Therefore, when common salt is exposed to air, there is no chemical reaction taking place.

Option 2 states that coal is burnt in air. This situation does result in a chemical reaction known as combustion. When coal is burnt in the presence of oxygen, it undergoes a chemical reaction called combustion, producing carbon dioxide, water, and releasing energy.

Option 3 mentions that sodium is placed in water. This situation does lead to a chemical reaction. When sodium reacts with water, it undergoes a vigorous reaction, producing hydrogen gas and sodium hydroxide.

Option 4 states that iron is kept in moist air. This situation does result in a chemical reaction. When iron is exposed to moisture in the air, it undergoes a chemical reaction called oxidation, forming iron oxide or rust.

Therefore, the correct answer is option 1, as in that situation, a chemical reaction does not occur.