A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

How would you distinguish experimentally between an alcohol and a carboxylic acid?

Would you be able to check if water is hard by using a detergent?

People use a variety of methods to wash clothes. Usually, after adding the soap, they 'beat' the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?