What is the respective number of $\alpha$ and $\beta$ particles emitted in the following radioactive decay: ${}_{90}^{200}X \to {}_{80}^{168}Y$?

The acceptable level of carbon monoxide gas $(CO)$ in the atmosphere in $ppm$ level is

$A$ 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:

True coelom appeared first in the course of evolution in

Statement $S$: Presence of a rigid cell wall and nucleoprotein as genetic material.
Statement $R$: Examples include $Euglena$,$Dinoflagellates$,$Amoeba$,and $Paramecium$.

$A$ solid sphere of radius $r$ made of a soft material of bulk modulus $K$ is surrounded by a liquid in a cylindrical container. $A$ massless piston of area $a$ floats on the surface of the liquid,covering the entire cross-section of the cylindrical container. When a mass $m$ is placed on the surface of the piston to compress the liquid,the fractional decrement in the radius of the sphere $\left( \frac{dr}{r} \right)$ is