Choose the option without an error :- 

Love is a beautiful emotion. 

he grammatically correct sentence is:

Love is a beautiful emotion.

The other three sentences are not grammatically correct:

• The love is the beautiful emotion. The word "the" is not needed before "love" in this sentence.
• The love is an emotion. The article "an" is not used before nouns that are not countable. "Love" is an uncountable noun.
• The love is a natural emotion. The article "a" is used before nouns that are countable. "Love" is an uncountable noun.