Which structure acts as the pacemaker of the heart?

Breeding crops with higher levels of vitamins,minerals,and proteins is known as ..........

If the direction cosines of two lines satisfy the equations $l+m+n=0$ and $2lm+2ln-mn=0$,then the acute angle between those two lines is

Two adjacent sides of a parallelogram $ABCD$ are given by $\overline{AB}=2 \hat{i}+10 \hat{j}+11 \hat{k}$ and $\overline{AD}=-\hat{i}+2 \hat{j}+2 \hat{k}$. The side $AD$ is rotated by an acute angle $\alpha$ in the plane of the parallelogram so that $AD$ becomes $AD^{\prime}$. If $AD^{\prime}$ makes a right angle with side $AB$,then the cosine of the angle $\alpha$ is given by

Liquids $A$ and $B$ form an ideal solution. If $X_A$ and $Y_A$ are the mole fractions of $A$ in the solution and in vapour phase in equilibrium,respectively,then (Given $P_A^o > P_B^o$):

Consider the following statements $A$ and $B$. Identify the correct choice in the given answer.
$A$. $p-n, p-p$ and $n-n$ forces between nucleons are not equal and charge dependent.
$B$. In a nuclear reactor,the fission reaction will be in an accelerating state if the value of the neutron reproduction factor $k > 1$.