USE the article 'an' before a singular noun beginning with a vowel sound.Ex: The jury will HOLD an emergency meeting half an hour before announcing its decision.Here, Hour is a singular noun beginning with a vowel sound. So, the correct article to be used here is An.Hence, option 2 is the correct answer. Exceptions: CHOOSING A or AnThere are a few exceptions to the general rule of using 'a' before words that start with consonants and 'an' before words that begin with vowels.The first letter of the word honour, for example, is a consonant, but it’s unpronounced. In spite of its spelling, the word honour begins with a vowel sound. Therefore, we use 'an'.My mother is an HONEST woman.She isaUnited States SENATOR.