Magnifying power of a simple microscope is (when final image is formed at $D = 25 \ cm$ from eye)

The following compounds have been arranged in order of their increasing thermal stabilities. Identify the correct order.
$I.$ $K_2CO_3$ $II.$ $MgCO_3$
$III.$ $CaCO_3$ $IV.$ $BeCO_3$

$A$ wheel has an angular acceleration of $3.0\, rad/s^2$ and an initial angular speed of $2.00\, rad/s$. In a time of $2\, s$,it has rotated through an angle (in radians) of:

Which of the following statements is true regarding the industrial production of hydrogen gas from water gas $(CO + H_2)$?

Four massless springs whose force constants are $2k, 2k, k$ and $2k$ respectively are attached to a mass $M$ kept on a frictionless plane (as shown in figure). If the mass $M$ is displaced in the horizontal direction,then the frequency of oscillation of the system is

$100$ coplanar forces,each equal to $10 \, N$,act on a body. Each force makes an angle of $\pi / 50$ with the preceding force. What is the resultant of the forces? $(N)$