Which of the following is a Lewis acid?

$A$ small source of sound vibrating at a frequency $500 ~Hz$ is rotated along a circle of radius $\frac{100}{\pi} ~cm$ at a constant angular speed of $5 ~revolutions ~per ~second$. The minimum and maximum frequency of the sound observed by a listener situated in the plane of the circle is (speed of sound is $332 ~ms^{-1}$).

$A$ square loop of area $25 \, cm^2$ has a resistance of $10 \, \Omega$. This loop is placed in a uniform magnetic field of magnitude $40 \, T$. The plane of the loop is perpendicular to the magnetic field. The work done in pulling the loop out of the magnetic field slowly and uniformly in one second will be:

The equation of the pair of straight lines parallel to the $X$-axis and touching the circle $x^2+y^2-6x-4y-12=0$ is:

Which of the following is the simplest amino acid?

Which of the following is known as the pitcher plant?