$A$ pair of perpendicular straight lines passes through the origin and also through the point of intersection of the curve $x^2+y^2=4$ with $x+y=a$. The set containing the value of $a$ is

$A$ particle undergoes uniform circular motion. About which point on the plane of the circle will the angular momentum of the particle remain conserved?

Two long conductors,separated by a distance $d$,carry currents $I_1$ and $I_2$ in the same direction. They exert a force $F$ on each other. Now,the current in one of them is increased to two times its original value and its direction is reversed. The distance between them is also increased to $3d$. The new value of the force between them is

Which one of the following elements shows the maximum number of different oxidation states in its compounds?

The structure of $IF_7$ is $......$ .

An infinitely long straight conductor is bent into the shape as shown below. It carries a current of $I$ ampere and the radius of the circular loop is $R$ metre. Then,the magnitude of magnetic induction at the centre of the circular loop is