The correct option is
C No article, the, the
Use of article is usually omitted before nouns, which are names of uncountable substances (Eg: sugar, water). Hence, no article is to be used before the word, 'water' in the first blank. Hence, options A and B are incorrect.
The word, 'elixir' means 'a magical or medicinal potion'. The definite article, 'the' is used before names of things to give the force of a superlative adjective. In the given sentence, 'Water is the elixir of life' means 'Water is the best magical potion of life'. Hence, the definite article, 'the' is to be used before the word, 'elixir'.
In the given sentence, 'water of this pond' refers to the specific water of the pond being indicated by the words, 'this pond'. The definite article, 'the' is used when we talk about a particular noun. Hence, 'the' is the article to be used before the phrase, 'water of this pond'. Hence, option C is correct.
The indefinite articles, 'a' and 'an' are not used when the noun being described is definite or specific. These cannot be used before the phrase, 'water of this pond' Hence, option D is incorrect.