Only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels. The term is commonly used for the energy levels of electrons in atoms, ions, or molecules, which are bound by the electric field of the nucleus, but can also refer to energy levels of nuclei or vibrational or rotational energy levels in molecules. The energy spectrum of a system with such discrete energy levels is said to be quantized
Answer:
Neutral carbon-12 (or any carbon atom) has 6 electrons with a total negative charge of 6e- orbiting a nucleus with a total positive charge of 6e+, so that the total net charge is zero. The nucleus is made up of 6 protons, each with a positive charge of e+, and 6 neutrons, each with zero charge.
Explanation:
Answer 1)

+

----> 2 HCl
This is a pure
chemical reaction that is taking place.
In this reaction the two chemical species which are Chlorine and Hydrogen undergo addition reaction and form two moles of hydrochloric acid. No new species is formed except the combination of reactants which gives the product.
Answer 2) H + H ----> He + n
This is a nuclear reaction.
As the reactant species is undergoing a reaction which is resulting in formation of new species completely different than the elements in reactants.
Also there is a neutron which is generated after the reaction this is clear indication of nuclear fusion reaction. Hence, it can be called as nuclear reaction.
Answer : Malik's experiment included to create artificial atmospheric oxygen; in order to perform experiment on red-legged grasshopper for growing it larger than normal, the part of recreating or mimicking the artificial oxygen for the experiment with additional 10% increase seems to be bit difficult and this may create a problem in defining the accuracy and precision for the experiment.
Chemical change. The heat from frying an egg causes the egg's protein to change permanently in texture and in appearance through a process.