Answer:
The correct option is C.
Explanation:
The given expression is
![x^2+16y^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/30odyakyzu5tmuvccdze3isyo61n4vbyt8.png)
In option A,
![(x+4y)(x+4y)=x^2+4xy+4xy+16y^2=x^2+8xy+16y^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/vo4p151uii2knr7scceobk66wg8yabx808.png)
Therefore option A is incorrect.
In option B,
![(x+4y)(x-4y)=x^2-4xy+4xy-16y^2=x^2-16y^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/1k8e35kfdnxy87v2lf27fakafmrzxrcr93.png)
Therefore option B is incorrect.
In option D,
![(x-4y)(x-4y)=x^2-4xy-4xy-16y^2=x^2-8xy+16y^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/jxkfw9bu4pk4zhkk5gb05puzlw54vvn2fe.png)
Therefore option D is incorrect.
Since the given expression can not be factored further, therefore it is a prime expression and option C is correct.