Which one of the following animals is correctly matched with its particular named taxonomic category?

$A$ certain metallic surface is illuminated with monochromatic light of wavelength $\lambda$. The stopping potential for the photoelectric current for this light is $3V_0$. If the same surface is illuminated with light of wavelength $2\lambda$,the stopping potential is $V_0$. The threshold wavelength for this surface for the photoelectric effect is:

If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k$ is equal to

To which family does $Ricinus$ $communis$ belong?

Select the incorrect order.

$A$ glass convex lens is of refractive index $1.55$ with both faces of same radius of curvature. What will be the radius of curvature if the focal length is to be $20 \text{ cm}$ (in $\text{ cm}$)?