What is the fourth proportional to$$\sqrt{6}, \sqrt{8}, \sqrt{21}$$ ?

Correct option is B

Concept Used:

​$$\text{Fourth proportional} = \frac{b \times c}{a} \\[10pt]$$​​

Solution:

​$$\text{Fourth Proportional}= \frac{\sqrt{8} \times \sqrt{21}}{\sqrt{6}} = 2\sqrt{7}$$​​