Ingredients used in making soap:
Soap is made through a chemical process called saponification, which involves the reaction of fats or oils with a strong alkali. The alkali used in soap-making is usually either sodium hydroxide (NaOH) or potassium hydroxide (KOH). These alkalis react with the fatty acids present in the oils or fats, resulting in the formation of soap molecules.

Commonly used oils and alkalis:
- Cotton seed oil and KOH: Cotton seed oil is a commonly used oil in soap-making. When combined with potassium hydroxide (KOH), it undergoes saponification to produce soap. Therefore, option 'A' is a correct choice.
- Castor oil and NaOH: Castor oil is another common oil used in soap-making. It reacts with sodium hydroxide (NaOH) during saponification to form soap. Hence, option 'C' is also a correct choice.
- Mustard oil and NaOH: Mustard oil is a type of oil that can be used in soap-making. It undergoes saponification with sodium hydroxide (NaOH) to produce soap molecules. Therefore, option 'D' is also a correct choice.

Explanation of the correct answer:
- Soybean oil and Ca(OH)2: Soybean oil is indeed used in soap-making and can undergo saponification with sodium hydroxide (NaOH). However, the given option states the use of calcium hydroxide (Ca(OH)2) instead of sodium hydroxide. Calcium hydroxide is not commonly used in soap-making, and its reaction with soybean oil would not result in the formation of soap molecules. Therefore, option 'B' is the correct answer as it includes an incorrect alkali for soap-making.

In conclusion:
The correct answer is option 'B', Soybean oil and Ca(OH)2. While soybean oil can be used in soap-making, the use of calcium hydroxide (Ca(OH)2) as stated in the option is incorrect. The other options (A, C, and D) are all valid combinations of oils and alkalis commonly used in soap production.