Which of the following is used to distinguish between ethylene and acetylene?

$300 \text{ g}$ of water at $25^{\circ} \text{C}$ is added to $100 \text{ g}$ of ice at $0^{\circ} \text{C}$. The final temperature of the mixture will be (in $^{\circ} \text{C}$)

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

Which is the smallest blood vessel in the body?

$A$ circle of radius $4$,drawn on a chord of the parabola $y^2 = 8x$ as diameter,touches the axis of the parabola. Then,the slope of the chord is

$A$ vibrating string of certain length $l$ under a tension $T$ resonates with a mode corresponding to the first overtone (third harmonic) of an air column of length $75\, cm$ inside a tube closed at one end. The string also generates $4\, beats$ per second when excited along with a tuning fork of frequency $n$. Now when the tension of the string is slightly increased,the number of beats reduces to $2\, per second$. Assuming the velocity of sound in air to be $340\, m/s$,the frequency $n$ of the tuning fork in $Hz$ is