Atoms, because molecules are a group of two or more atoms stuck together :)
On absorbing energy, an electron moves to an excited state (unstable state) from its ground state (stable state). Since the electron is in unstable state so it tends to rearrange itself to return to its lowest energy state. On returning to lowest energy state which is stable, it releases energy in the form of light.
Hence, option A that is the electron releases energy in the form of light on falling to lower energy state from excite state.
Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. There are two main types of boiling; nucleate boiling where small bubbles of vapour form at discrete points, and critical heat flux boiling where the boiling surface is heated above a certain critical temperature and a film of vapor forms on the surface. Transition boiling is an intermediate, unstable form of boiling with elements of both types. The boiling point of water is 100 °C or 212 °F, but is lower with the decreased atmospheric pressure found at higher altitudes.
Boiling water is used as a method of making it potable by killing microbes that may be present. The sensitivity of different micro-organisms to heat varies, but if water is held at 70 °C (158 °F) for ten minutes, many organisms are killed, but some are more resistant to heat and require one minute at the boiling point of water. Clostridium spores can survive this treatment, but as the infection caused by this microbe is not water-borne, this is not a problem.
Boiling is also used in cooking. Foods suitable for boiling include vegetables, starchy foods such as rice, noodles and potatoes, eggs, meats, sauces, stocks and soups. As a cooking method it is simple and suitable for large scale cookery. Tough meats or poultry can be given a long, slow cooking and a nutritious stock is produced. Disadvantages include loss of water-soluble vitamins and minerals. Commercially prepared foodstuffs are sometimes packed in polythene sachets and sold as "boil-in-the-bag" products.
The type of atoms present in the chemical compound and the proportion or how many specific atoms are respect to other atoms in the chemical compound.
