$X$-rays are used in:

In a compound microscope,the focal lengths of two lenses are $1.5 \, cm$ and $6.25 \, cm$. An object is placed at $2 \, cm$ from the objective lens and the final image is formed at $25 \, cm$ from the eye lens. The distance between the two lenses is.......$cm$.

Which of the following is the most important cause for the extinction of animals and plants?

The cubic equation whose roots are thrice to each of the roots of $x^3+2 x^2-4 x+1=0$ is

The oxidation number of $Pt$ in $[Pt(C_2H_4)Cl_3]^-$ is

If $\vec{a}, \vec{b}, \vec{c}$ are mutually perpendicular vectors having magnitudes $1, 2, 3$ respectively,then $[\vec{a}+\vec{b}+\vec{c} \quad \vec{b}-\vec{a} \quad \vec{c}]=$