It’s a unity. We use “a” or “an” based on the sound made by the initial letter of the noun that follows, not on how it is spelled. The initial letter of the word “unity” makes a “you” sound; therefore, it takes the indefinite article “a”.

It’s a unit. The rule for using “a” or “an” is based on pronunciation, not spelling.

It’s a unique. The rule for determining whether to use “a” or “an” is based on pronunciation, not spelling. Since the initial letter of the word unique produces a consonant sound (a “you” sound), it takes the indefinite article “a”.

It’s “a unifying”. Starting with a consonant sound (you), the word unifying takes the indefinite article “a”. Remember, the rule for using “a” or “an” is based on pronunciation, not spelling.

It’s a unified. The rule for using “a” or “an” is based on pronunciation, not spelling. Since the word “unified” begins with the sound “you”, it takes the indefinite article “a”.

It’s a unification. The rule for using “a” or “an” is that we use “a” before a consonant sound and “an” before a vowel sound. The word “unification” starts with a consonant sound since its first letter (u) sounds like “you”.

It’s a united. Use "a" before words which sound like they start with a consonant, even if the first letter is a vowel. The word united begins with a consonant sound (you), so it takes the article “a”.

It’s a union. We use “a” with nouns that start with a consonant sound. Sometimes, as in the case of “union”, a word begins with the vowel “u” in the spelling, but with a consonant in the pronunciation (you).

It’s a unicorn. The word “unicorn” begins with a vowel in the spelling, but it makes a consonant sound (a "you" sound).