Dehydration of ethanol to form an ether is a chemical reaction that involves the removal of a water molecule from ethanol. This reaction is typically catalyzed by an acid or a base. In this case, the most suitable requirement for the dehydration of ethanol to form an ether is option 'A', which is sulphuric acid at 413K.

1. Dehydration Reaction:
The dehydration of ethanol involves the removal of a water molecule (H2O) from ethanol (C2H5OH) to form an ether (C2H5OC2H5). This reaction can be represented as follows:
C2H5OH -> C2H5OC2H5 + H2O

2. Catalysis:
The reaction requires a catalyst to facilitate the removal of the water molecule. In this case, both sulphuric acid (H2SO4) and sodium hydroxide (NaOH) can act as catalysts for the dehydration of ethanol. However, the most suitable catalyst for this reaction is sulphuric acid.

3. Temperature:
The temperature at which the reaction is carried out also affects the rate and selectivity of the reaction. Option 'A' specifies a temperature of 413K, which is relatively lower compared to option 'B' (443K). Lower temperatures are generally preferred for this reaction as they help in achieving a higher yield of the desired product.

4. Sulphuric Acid:
Sulphuric acid is a strong acid that can act as a catalyst for the dehydration of ethanol. It protonates the hydroxyl group of ethanol, making it a better leaving group. This facilitates the removal of a water molecule and formation of the ether. Sulphuric acid also helps in maintaining the acidity of the reaction medium, which is important for the catalytic activity.

In conclusion, the most suitable requirement for the dehydration of ethanol to form an ether is sulphuric acid at 413K. This combination provides the optimal conditions for the reaction, resulting in a higher yield of the desired ether product.