Which of the following is the value of

$(\sqrt{11}-\sqrt{7})(\sqrt{11}+\sqrt{7})$

$=(\sqrt{11})^{2}-(\sqrt{7})^{2} \quad\left[(a-b)(a+b)=a^{2}-b^{2}\right]$

$=11-7$

$=4$

Hence, the correct answer is option (b).