Boron in green plants assists in

The dispersive powers of the materials of two lenses forming an achromatic combination are in the ratio of $4: 3$. If the effective focal length of the two lenses is $+60 ~cm$,then the focal lengths of the lenses should be:

$A$ vertical mass-spring system executes simple harmonic oscillations with a period of $2\,s$. $A$ quantity of this system which exhibits simple harmonic variation with a period of $1\,s$ is

In angiosperms,the functional megaspore develops into:

In the following common emitter circuit,if $\beta = 100$,$V_{CE} = 7 \, V$,$V_{BE} = \text{Negligible}$,and $R_C = 2 \, k\Omega$,then find $I_B$ in $mA$.

Which of the following statements is correct?