$A$ uniform beam of weight $W$ is attached to a vertical wall by a hinge $H$. The beam is held horizontal by a rope as shown below. Which one of the following best shows the direction of the reaction force $R$ at the hinge?

$A$ block of mass $M_1$ is hung by a light spring of force constant $k$ from the top bar of a reverse $U$-frame of mass $M_2$ resting on the floor. The block is pulled down from its equilibrium position by a distance $x$ and then released. The minimum value of $x$ such that the reverse $U$-frame will leave the floor momentarily is:

Which of the following pairs of elements cannot form an alloy?

In a $CE$ transistor amplifier,the audio signal voltage across the collector resistance of $2\, k\Omega$ is $2\, V$. If the base resistance is $1\, k\Omega$ and the current amplification factor $(\beta)$ of the transistor is $100$,the input signal voltage is:

The yellow colour solution of $Na_2CrO_4$ changes to orange-red on passing $CO_2$ gas due to the formation of

Nitrobenzene on reduction with zinc and $NH_4Cl$ gives