Correct answer is (d) 0
The explanation: Coefficient is the number which is multiplied with respective variable.
In the given polynomial 6x^4 + 3x^2 + 8x + 5, there is not an expression containing x^3. So we can write 6x^4+ 3x^2+8x+5 as 6x^4 + 0x^3 + 3x^2 + 8x + 5. We can see that 0 is multiplied with expression x^3, so coefficient of x^3 is 0.