Biquadratic reduction

Given:

$$x^{4} - ax^{2} + 9 = 0$$

Let $$t = x^2$$ $$\Rightarrow$$ $$t^2 = x^4$$

$$\Rightarrow$$ $$t^2 - at + 9 = 0$$

Now all roots are real and distinct,

$$\therefore$$ $$ D > 0$$

$$\Rightarrow$$ $$a^2 - 36 > 0$$

$$\Rightarrow$$ $$ a > 6$$ OR $$ a < -6$$

We want smallest positive integral value of $$a$$

$$\therefore$$ $$a > 6$$

Smallest positive integral value of $$a$$ is $$7$$

Thus, option B is the correct choice.