Which of the following has the highest dipole moment?

An oxide of an element is a gas and dissolves in water to give an acidic solution. The element belongs to

The abscissae of $A$ and $B$ are the roots of the equation $x^2+2ax-b^2=0$ and their ordinates are the roots of the equation $y^2+2py-q^2=0$. Find the equation of the circle with $AB$ as the diameter.

The shield-shaped cotyledon seen in monocot seeds is known as:

In the following structure,the double bonds are marked as $I, II, III$ and $IV$. Geometrical isomerism is not possible at site$(s)$:

Which of the following ions does not exist in an aqueous solution?