In which type of crops is the mass selection method used?

In Young's double slit experiment,the seventh maximum with wavelength ${\lambda _1}$ is at a distance $d_1$ from the central maxima,and the same maximum with wavelength ${\lambda _2}$ is at a distance $d_2$. Then the ratio $d_1/d_2$ is:

Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?

$x$ grams of calcium carbonate was completely burnt in air. The weight of the solid residue formed is $28 \text{ g}$. What is the value of $x$ (in grams)?

At $25^{\circ} C$, the concentration of $H ^{+}$ions in $1.00 \times 10^{-3} M$ aqueous solution of a weak monobasic acid having acid dissociation constant $\left(K_a\right)=4.00 \times 10^{-11}$ is $X \times 10^{-7} M$. The value of $X$ is $...$ .
Use: Ionic product of water $\left(K_w\right)=1.00 \times 10^{-14}$ at $25^{\circ} C$

Two bodies $A$ and $B$ of equal mass are suspended from two separate massless springs of force constant $k_{1}$ and $k_{2}$ respectively. The bodies oscillate vertically such that their maximum velocities are equal. The ratio of the amplitudes of body $A$ to that of body $B$ is