What is the percentage of Photosynthetically Active Radiation $(PAR)$ in the incident solar radiation?

Electrovalent bond formation depends on

$A$ particle moves along a circle of radius $\frac{20}{\pi} \; m$ with constant tangential acceleration. If the velocity of the particle is $80 \; m/s$ at the end of the second revolution after motion has begun,the tangential acceleration is:

The value of $k$ such that the lines $2x - 3y + k = 0$,$3x - 4y - 13 = 0$,and $8x - 11y - 33 = 0$ are concurrent,is

$A$ regular polygon of $n$ sides has $170$ diagonals,then $n$ is equal to

Which of the following is the characteristic outer electronic configuration of alkaline earth metals?