Two identical flutes produce fundamental notes of frequency $300 \ Hz$ at $27^{\circ}C.$ If the temperature of air in one flute is increased to $31^{\circ}C,$ the number of beats heard per second will be

The image formed by a convex mirror of focal length $30 \ cm$ is a quarter of the size of the object. The distance of the object from the mirror is $... \ cm$.

Match the Column-$I$ with Column-$II$ and select the correct option from the options given below:

Column-$I$ (Disease)	Column-$II$ (Pathogen)
$(A)$ Citrus canker	$(P)$ Protozoa
$(B)$ Malaria	$(Q)$ Fungi
$(C)$ Rust of wheat	$(R)$ Viroid
$(D)$ Bovine spongiform encephalopathy	$(S)$ Bacteria
-	$(T)$ Prions

The contrapositive of the statement 'If two numbers are not equal,then their squares are not equal' is:

The $P-V$ diagram of $2\,g$ of helium gas for a certain process $A \to B$ is shown in the figure. What is the heat given to the gas during the process $A \to B$ (in $P_0V_0$)?

The following are some statements related to $VA$ group hydrides:
$I$. Reducing property increases from $NH_3$ to $BiH_3$.
$II$. Tendency to donate lone pair decreases from $NH_3$ to $BiH_3$.
$III$. Thermal stability of hydrides decreases from $NH_3$ to $BiH_3$.
$IV$. Bond angle of hydrides decreases from $NH_3$ to $BiH_3$.
The correct statements are: