The amino acid which is not optically active is

Which of the following statements is correct?

$\sqrt{10 - \sqrt{24} - \sqrt{40} + \sqrt{60}} = ?$

If the pair of lines given by $(x^2+y^2) \cos^2 \theta = (x \cos \theta + y \sin \theta)^2$ are perpendicular to each other,then $\theta$ is equal to

Which of the following ethers is a liquid at room temperature?

$A$ satellite is launched into a circular orbit of radius $R$ around the Earth,while a second satellite is launched into an orbit of radius $1.02 R$. The percentage difference in the time periods of the two satellites is ......... $\%$