Using the words an and a does not depend on the spelling of the word it comes before, it depends on the pronunciation of the word.
In most cases, an is used before words that begin with vowels (a, e, i, o, u).
We should say 'an' hour (because hour begins with a vowel sound) and 'a' history (because history begins with a consonant sound).
Similarly, you should say 'a' union even if union begins with a 'u'. That is because the pronunciation begins with 'yu', which is a consonant sound.
Look at the examples of the word an below:
Look at the examples of the word a below:
Now it’s time to start the activities!
Decide whether 'an' or 'a' is needed to complete the sentences.
Remember, it is the sound, not the spelling which is important.