The ascending order of distance between foci for the ellipses.

It is not possible to measure the atomic radius precisely since the electron cloud surrounding the atom doesnot have sharp boundary. One practical approach to estimate the size of an atom of a non-metallic element is to measure the distance between two atoms when they are bound together by a single bond in a covalent molecule and then dividing by two. For metals we define the term "metallic radius" which is taken as half the internuclear distance separating the metal cores in the metallic crystal. The vander Waal's radius represents the overall size of the atoms which includes its valence shell in a nonbonded situation. It is the half of the distance between two similar atoms in separate molecules in a solid. The atomic radius decreases across a period and increases down the group. Same trends are observed in case of ionic radius. Ionic radius of the species having same number of electrons depends on the number of protons in their nuclei. The correct order of radii is

The contact angle between a solid and a liquid is a property of