For a crystal,the angle of diffraction $(2 \theta)$ is $90^{\circ}$ and the second order line has a $d$ value of $2.28 \ \mathring{A}$. The wavelength (in $\mathring{A}$) of $X$-rays used for Bragg's diffraction is

The simplest formula of a compound containing $50\%$ of element $X$ (atomic mass $10$) and $50\%$ of element $Y$ (atomic mass $20$) is

Cycas leaflets are

$Mg$ is obtained by:

When a body of mass $1.0 ~kg$ is suspended from a certain light spring hanging vertically,its length increases by $5 ~cm$. By suspending a $2.0 ~kg$ block to the spring,if the block is pulled through $10 ~cm$ and released,the maximum velocity in $m/s$ is: (Acceleration due to gravity $= 10 ~m/s^2$)

$\Delta \lambda$ is the difference between the wavelength of the $K_{\alpha}$ line and the minimum wavelength of the continuous $X$-ray spectrum when the $X$-ray tube is operated at a voltage $V$. If the operating voltage is changed to $V/3$,then the above difference is $\Delta \lambda^{\prime}$. Then: