Ideal gasses (ideal gas law)
Answer : Option D) Covalent bond.
Explanation : The bond formed when electrons are shared is called a covalent bond.
A covalent bond which is also called as molecular bond, is a chemical bond which involves mainly the sharing of electron pairs between atoms. These electron pairs are called as shared pairs or bonding pairs, which are stable balance of attractive and repulsive forces between atoms, when these bonding pairs share electrons, it is called as covalent bonding.
Covalent bonding is usually seen in non-metals which share their electrons while bonding.
Answer : Option C) Atomic Size
Explanation : The atomic radius of the elements is found to be decreasing if we go from left to right in the modern periodic table. Accordingly, 
increases as the number of shielding electrons present in the atomic nucleus of the periodic elements which lies in the same row remains constant while the number of protons in each atomic shell increases.
The effective nuclear charge of an atom is defined as the net positive charge which is felt by the valence electron of the atomic element.
When 
is observed to decrease, it is seen that the atomic radius grows in size. So, it explains the inverse relationship between both. This phenomenon occurs, because there is more screening of the electrons from the nucleus taking place, which is observed due to decrease the attraction between the electron and the nucleus.
Answer: Solids
Explanation:
Solids have a definite volume and structure. These are comprised of atoms, ions, and molecules closely packed together giving a confined structure to the solids. The particles are bound with strong force of attraction. The particles in the solid are arranged in an repeated, orderly, and three dimensional pattern. Depending upon the substance of the solid the particles within the solid can be ions, atoms, and can be molecules.
