The verb, 'upset' in the given sentence means "knocked something over". As the kettle was knocked off, the boiling water would have spilt on her hand and injured it.
Option A: The verb, 'scorched' means "caused something to change colour with flame/ dry heat". In the given sentence, there is no dry heat as the boiling water (a liquid) has injured her hand. Hence, this option is not correct.
Option B: The verb, 'scalded' means 'injured with very hot liquid or steam'. In the given sentence, boiling water (very hot liquid) injured her hand. Hence, this option is most appropriate and option B is the correct answer.
Option C: The verb, ‘sizzled’ is the past tense of the verb, 'sizzle'. 'Sizzle' is an action word used for food when it 'makes a hissing sound when fried or cooked'. Here, water is not a food item. It was not cooked/ fried either. Hence, this option is not correct.
Option D: The verb, ‘smouldered' means; burned slowly with smoke, but no flame'. Boiling water causes water vapour to be released, but not smoke. Hence, this option is not correct.