Most of the endangered species are the victims of

The dispersive powers of the materials of two lenses forming an achromatic combination are in the ratio of $4: 3$. If the effective focal length of the two lenses is $+60 ~cm$,then the focal lengths of the lenses should be:

One gas bleaches the colour of flowers by reduction,while the other by oxidation,the two gases respectively are

Two identical charged spherical drops, each of capacitance $C$, merge to form a single drop. The resultant capacitance is:

Portland cement is manufactured using which of the following?

In which of the following is the hydration energy higher than the lattice energy?