If the angle $2 \theta$ is acute,then the acute angle between the pair of straight lines $x^2(\cos \theta - \sin \theta) + 2xy \cos \theta + y^2(\cos \theta + \sin \theta) = 0$ is:

Which of the following vitamins is water-soluble?

In an unbiased $p-n$ junction,holes diffuse from the $p-$ region to $n-$ region because

The equation of a stationary wave along a stretched string is given by $y = 5 \sin \frac{2\pi}{3}x \cos 40\pi t$,where $x$ and $y$ are in $cm$ and $t$ is in $s$. The separation between two adjacent nodes is ..... $cm$.

The strongest acid among the following is:

$A$ mass $M$ attached to a horizontal spring executes $S.H.M.$ of amplitude $A_1$. When the mass $M$ passes through its mean position,a smaller mass $m$ is placed over it and both of them move together with amplitude $A_2$. The ratio $\left(\frac{A_1}{A_2}\right)$ is