In how many ways can $8$ identical balls be distributed into $3$ distinct boxes such that no box remains empty?

The structure of $PCC$ is

In pea plants,yellow seeds are dominant over green seeds. If a heterozygous yellow-seeded plant is crossed with a green-seeded plant,what ratio of yellow to green-seeded plants would you expect in the $F_1$ generation?

The two surfaces of a concave lens,made of glass of refractive index $1.5$,have the same radii of curvature $R$. It is now immersed in a medium of refractive index $1.75$. Then the lens:

$A$ liquid does not wet the solid surface if the angle of contact is

The vectors $\overrightarrow{AB} = 3\hat{i} + 4\hat{k}$ and $\overrightarrow{AC} = 5\hat{i} - 2\hat{j} + 4\hat{k}$ are the sides of a triangle $ABC$. The length of the median through $A$ is