Which of the following is an oxidizing agent?

In a biprism experiment,if the $5^{\text{th}}$ bright band with wavelength $\lambda_{1}$ coincides with the $6^{\text{th}}$ dark band with wavelength $\lambda_{2}$,then the ratio $\left(\frac{\lambda_{2}}{\lambda_{1}}\right)$ is:

In $\Delta ABC,$ if $\cos A + \cos C = 4\sin^2\frac{B}{2},$ then $a, b, c$ are in

The reagent used for converting acetylene to oxalic acid is

The total revenue in Rupees received from the sale of $x$ units of a product is given by $R(x) = 3x^2 + 36x + 5$. The marginal revenue,when $x = 15$,is

Which role is played by Lactobacillus in our stomach?