Which metal is protected by a layer of its own oxide?

Which of the following pairs contains structurally similar substances?

If $(1, a)$ and $(b, 2)$ are conjugate points with respect to the circle $x^2+y^2=25$,then $4a+2b$ is equal to

The part of the castor seed from which oil is obtained is called the .....

The electronic configurations of four elements are given as:
$(I) 1s^2, (II) 1s^2 2s^2 2p^2, (III) 1s^2 2s^2 2p^5, (IV) 1s^2 2s^2 2p^6$. Which configuration has the ability to form both ionic and covalent bonds?

Which of these is least likely to act as a Lewis base?