Which era is known as the age of birds and mammals?

The variation of magnetic susceptibility $(\chi )$ with temperature for a diamagnetic substance is best represented by

Flux $\phi$ (in weber) in a closed circuit of resistance $10\,\Omega$ varies with time $t$ (in sec) according to the equation $\phi = 6t^2 - 5t + 1$. What is the magnitude of the induced current at $t = 0.25\,s$ (in $,A$)?

The variance of the first $50$ even natural numbers is

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:

The reagent used in the Wolff-Kishner reduction is