Which of the following statements is incorrect?

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

The solution of $\cos y + (x \sin y - 1) \frac{dy}{dx} = 0$ is

The solution of $\frac{dy}{dx} = (\frac{x}{y})^{-1/3}$ is

If $(h, k)$ is the image of the point $(2, -3)$ with respect to the line $5x - 3y = 2$,then $h + k$ is equal to

Given below are two statements:
Statement $I$: $[CoBr_{4}]^{2-}$ ion will absorb light of lower energy than $[CoCl_{4}]^{2-}$ ion.
Statement $II$: In $[CoI_{4}]^{2-}$ ion, the energy separation between the two sets of $d$-orbitals is more than $[CoCl_{4}]^{2-}$ ion.
In the light of the above statements, choose the correct answer from the options given below: