Questions

A conjunction is a word that joins words, clauses, phrases or sentences.

For example but, and, or, nor, yet for, so, although, since, because, unless, when, where, while, etc.

There are four types of conjunctions:

1. Subordinating Conjunction

2. Correlative Conjunction

3. Phrasal Conjunction

4. Coordinating Conjunction

In the given sentence, "She is not only a great singer but also an exceptional dancer" Not Only But Also is a type of Correlative conjunction.

From all the hints given, 

only 042 satisfies and it unlocks the key.

A fool’s errand means a task that has little to no chance of being successful or beneficial.

Here all the given options are Exothermic reactions. Exothermic reactions are those reactions which involves the release of heat.

Generally all the combining reactions are exothermic in nature.