Which gas is produced during the process of fermentation that causes effervescence?

Look at the figure and answer the following questions:
$(a)$ What change would you observe in the calcium hydroxide solution taken in tube $B$?
$(b)$ Write the chemical reactions involved in test tubes $A$ and $B$ respectively.

Which substance,when added as an adulterant to ethanol used as an intoxicating drink,causes a person to lose their vision?

Draw the electron dot structure of ethyne and also draw its structural formula.

Write the name of the next homologue of $CH_{3}OH$ and $HCOOH$.

$(a)$ Differentiate between soap and detergent.
$(b)$ Explain why soaps form scum with hard water,whereas detergents do not.