She bought _________ gold ring.
She bought _________ gold ring.
Explanation
Article (a,an,the) are used before a noun.
The indefinite article is not used before an abstract or material noun.
Wrong: It is made of a gold.
Right: It is made of gold
Note: It is correct to say She bough a gold ring.
In the above expression, the material noun 'gold' has been used as adjective.