What is the wavelength of light with a frequency of $100\; Hz$?

Which of the following pairs is incorrect?

Which of the following ray diagrams shows physically possible refraction?

$A$ body of mass $1 ~g$ and carrying a charge $10^{-8} ~C$ passes through two points $P$ and $Q$. $P$ and $Q$ are at electric potentials $600 ~V$ and $0 ~V$,respectively. The velocity of the body at $Q$ is $20 ~cm/s$. Its velocity in $m/s$ at $P$ is:

$A$ screen is placed $50\,cm$ from a single slit,which is illuminated with $6000 \mathring{A}$ light. If the distance between the first and third minima in the diffraction pattern is $3\,mm$,the width of the slit is.....$mm$.

If we completely remove the decomposers from an ecosystem,its functioning will be adversely affected because