Identify the halogen exchange reaction from the following.

On what basis are the three types of lichens classified?

The maximum possible number of real roots of the equation $x^5 - 6x^2 - 4x + 5 = 0$ is

$A$ carrier signal $60 \sin(2\pi \times 10^6 t)$ is used to modulate an audio signal $15 \sin(300\pi t)$. The depth of modulation is .........$\%$.

The wavelength of $H_{\alpha}$ line of Balmer series is $X \ \mathring{A}$. What is the wavelength of $H_{\beta}$ line of Balmer series?

$A$ tuning fork of frequency $392 \ Hz$ resonates with $50 \ cm$ length of a string under tension $T$. If the length of the string is decreased by $2\%$,keeping the tension constant,the number of beats heard when the string and the tuning fork are made to vibrate simultaneously is: