The correct answer is D. Releif
Step-by-step explanation:
The word spelling refers to the letters that compose a word and the order these should have to be considered as correct. Because of this, when words are misspelled is because the letters in a word are not in the correct order, letters that are not correct have been added or letters have been omitted, which is a common mistake in writing. In the case of the sentence "Carol perceived a neigh of releif when the horse was unhitched from the heavy sleigh", the word whose letters are not in the correct order and therefore is a misspelled word or shows a mistake in spelling is "releif", because the correct word is written "relief" and means an alleviation feeling, while the word "releif" does not exist in English language.