Acetone on addition to methyl magnesium bromide forms a complex,which on decomposition with acid gives $X$ and $Mg(OH)Br$. Which one of the following is $X$?

Doctors use a stethoscope to hear the sounds produced during each cardiac cycle. The second heart sound is heard when:

The period of $f(x)=\cos \left(\frac{x}{3}\right)+\sin \left(\frac{x}{2}\right)$ is (in $pi$)

Which one of the following characters is not typical of the class Mammalia?

The minimum force required to start pushing a body up a rough (having coefficient of friction $\mu$) inclined plane is $F_1$,while the minimum force needed to prevent it from sliding down is $F_2$. If the inclined plane makes an angle $\theta$ with the horizontal such that $\tan \theta = 2\mu$,then the ratio $F_1 / F_2$ is

The molecular interactions responsible for hydrogen bonding in $HF$ are: