Hot concentrated sulphuric acid,on reaction with which one of the following elements,produces two gaseous products?

Assertion : The isothermal curves intersect each other at a certain point.
Reason : The isothermal change takes place slowly,so,the isothermal curves have very little slope.

If a polygon of $n$ sides has $275$ diagonals,then $n$ is equal to

Assertion: The ferromagnetic substance does not obey Curie's law.
Reason: At Curie point, a ferromagnetic substance starts behaving as a paramagnetic substance.

$A$ point object is placed at the centre of a glass sphere of radius $6 \, cm$ and refractive index $1.5$. The distance of the virtual image from the surface of the sphere is.....$cm$.

The resolving power of an astronomical telescope is $0.2\, sec$. If the central half portion of the objective lens is covered,the resolving power will be....$sec$