What is the cause of embryo formation from pollen grains in tissue culture medium?

Which one of the following correctly represents the variation of electronegativity $(EN)$ with atomic number $(Z)$ of group $13$ elements?

$A$ prism of refractive index $\mu$ and angle $A$ is placed in the minimum deviation position. If the angle of minimum deviation is $A$, then the value of $A$ in terms of $\mu$ is :

If $\sqrt{9 x^2+6 x+1} < (2-x)$,then:

Which one of the following is correct about the stability of the given ions?

If $\frac{1}{x^4+x^2+1}=\frac{A x+B}{x^2+x+1}+\frac{C x+D}{x^2-x+1}$, then $C+D$ is equal to