An oxidation number can be assigned to a given element or compound by following the following rules.

• Any free element has an oxidation number equal to zero.
• For monoatomic ions, the oxidation number always has the same value as the net charge corresponding to the ion.
• The hydrogen atom (H) exhibits an oxidation state of +1. However, when bonded with an element with less electronegativity than it, it exhibits an oxidation number of -1.
• Oxygen has an oxidation of -2 in most of its compounds. However, in the case of peroxides, the oxidation number corresponding to oxygen is -1.
• All alkali metals (group 1 elements) have an oxidation state of +1 in their compounds.
• All alkaline earth metals (group 2 elements) exhibit an oxidation state of +2 in their compounds.
• In the compounds made up of two elements, a halogen (group 17 elements) have an oxidation number of -1 assigned to them.
• In the case of neutral compounds, the sum of all the oxidation numbers of the constituent atoms totals to zero.
• When polyatomic ions are considered, the sum of all the oxidation numbers of the atoms that constitute them equals the net charge of the polyatomic ion.

Thus, the oxidation number of an atom in a given compound can be calculated with the steps mentioned above.

1. Valency is the maximum no. of electrons which an atom can lose or gain while oxidation no. is the actual no. of electrons which the element lose or gain to form a molecule.
2. Valency is the property of an isolated atom while oxidation state is calculated for an atom is present in a molecule i.e, in a bonded state.
3. Valency of an element remains the same while its oxidation state may be different in different molecules.

(a) We know that M = n/V or n = M × V ( in L)
n = 0.02 × 0.1 = 0.002
No.of molecules = n × 6.022 × 10²³
= 0.002 × 6.022 × 10²³ = 12.044 × 10²⁰ molecules 

Journalism is the activity of gathering, assessing, creating, and presenting news and information. It is also the product of these activities. Journalism can be distinguished from other activities and products by certain identifiable characteristics and practices.Journalism is unbiased production and distribution of reports on current or past events based on facts and supported with proofs or evidences. The word journalism applies to the occupation, as well as citizen journalists who gather and publish unbiased information based on facts and supported with proofs or evidences.

Gunmetal alloys contain roughly 88% copper, 8-10% tin, and 2-4% zinc. Lead can be added for ease of machining or for bearing alloys. "Naval brass", for use in seawater, contains 40% zinc but also 1% tin. Brass is a mixture of copper and zinc, which has a harder finish than copper alone. We supply brass to customers for a variety of applications due to its durability and looks.

Alcohols generally have higher boiling points in comparison to other hydrocarbons having equal molecular masses. This is due to the presence of intermolecular hydrogen bonding between hydroxyl groups of alcohol molecules. In general, the boiling point of alcohols increases with an increase in the number of carbon atoms in the aliphatic carbon chain. On the other hand, the boiling point decreases with an increase in branching in aliphatic carbon chains the Van der Waals forces decreases with a decrease in surface area. Thus primary alcohols have a higher boiling point.

One molecule of Ca(NO₃)₂ contains 2 atoms of N.

Mass of nitrogen in one mole Ca(NO₃)₂ molecule = 28 g ( 2 x molar mass of nitrogen)

28g  N  = one mole molecule of Ca(NO₃)_2.

20 g  N =  1x 20 /28 = 0.71 mole of Ca(NO₃)_2.

One molecule of Ca(NO₃)₂ contains 2 atoms of N.

1 mole  Ca(NO₃)₂  = 40 g  Ca

0.71 mole Ca(NO₃)₂ = 40 x 0.71 = 28.4 g Ca.

{tex}Momentum=3.313×10^-24kgms-{/tex}

Explanation:

Here,de-broglie wavelength.

wavelenght=h/mv

200× 10^-12=6.626×10^-34/p[1pm=10^-12m,h=6.626×10^-34]

p=6.626×10^-34/200×10^-12

p=6.626×10^-34/2×10^-10

p=3.313×10 ^-34+10

p=3.313×10^-24kgms-

A molecule is the smallest unit (particle) of a compound having the physical and chemical properties of that compound. This does not mean that molecules can not be broken down into smaller parts, e.g. the atoms from which they are formed or the fragments of the molecule, each consisting of several atoms or parts of atoms.

In 1900, a German scientist named Max Planck wrote an equation to show this the relationship between energy and frequency of electromagnetic radiation : 

E = hv

where E is the energy of a bit of light called a quantum, A quantum is the smallest bit of electromagnetic radiation that can be emitted.  It is also called a photon of light or small “packet” of electromagnetic radiation.    The “h” in the above equation is a very small constant called “Planck’s constant” (6.626068 × 10^-34 J s) and “n” is the frequency of the radiation.  Through various experiments of Planck and Albert Einstein, it came to be accepted that light has properties of particles as well as waves. Planck’s “quantum” idea became the basis for the modern understanding of atomic structure.  In the above equation, as the frequency of radiation increases, its energy increases by the increment “h”.  In other words, energy was not continuous, it was quantized – only certain energies are allowed.  Continuous energy and quantized energy can be likened to a  ramp versus a set of stairs connecting two levels of a building.   The ramp is analogous to continuous energy – you can sit at any position along the ramp and thus be at any elevation between the two levels.  The stairs are analogous to quantized or discrete energy – you can only sit at certain elevations between the two levels and nowhere in between.  You may sit only on the steps, not in between the steps.  Only certain elevations are allowed.

The discovery of the proton is credited to Ernest Rutherford, who proved that the nucleus of the hydrogen atom (i.e. a proton) is present in the nuclei of all other atoms in the year 1917.

• Ernest Rutherford observed that his scintillation detectors detected hydrogen nuclei when a beam of alpha particles was shot into the air.
• After investigating further, Rutherford found that these hydrogen nuclei were produced from the nitrogen atoms present in the atmosphere.
• He then proceeded to fire beams of alpha particles into pure nitrogen gas and observed that a greater number of hydrogen nuclei were produced.
• He concluded that the hydrogen nuclei originated from the nitrogen atom, proving that the hydrogen nucleus was a part of all other atoms.
• This experiment was the first to report a nuclear reaction, given by the equation: ¹⁴N + α → ¹⁷O + p [Where α is an alpha particle which contains two protons and two neutrons, and ‘p’ is a proton]
• The hydrogen nucleus was later named ‘proton’ and recognized as one of the building blocks of the atomic nucleus.

There are five basic laws of chemical combination that govern the chemical combinations of elements:

. Law of Conservation of Mass

In simple terms, this law states that matter can neither be created nor destroyed. In other words, the total mass, that is, the sum of the mass of reacting mixture and the products formed remains constant. Antoine Lavoisier gave this law in the year 1789 based on the data he obtained after carefully studying numerous combustion reactions.

2. Law of Definite Proportions

Joseph Proust, a French chemist stated that the proportion of elements by weight in a given compound will always remain exactly the same. In simple terms, we can say that irrespective of its source, origin or its quantity, the per cent composition of elements by weight in a given compound will always remain the same.

3. Law of Multiple Proportions

This law states that if two elements combine to form more than one compound, the masses of these elements in the reaction are in the ratio of small whole numbers. This law was given by Dalton in the year 1803.

4.  Gay Lussac’s Law of Gaseous Volumes

In 1808, Gay Lussac gave this law based on his observations. This law states that when gases are produced or combine in a chemical reaction, they do so in a simple ratio by volume given that all the gases are at the same temperature and pressure. This law can be considered as another form of the law of definite proportions. The only difference between these two laws of chemical combination is that Gay Lussac’s Law is stated with respect to volume while the law of definite proportions is stated with respect to mass.

5. Avogadro’s Law

Avogadro proposed this law in the year 1811. It stated that under the same conditions of temperature and pressure, an equal volume of all the gases contains an equal number of molecules. This implies that 2 litres of hydrogen will have the same number of molecules as 2 litres of oxygen given that both the gases are at the same temperature and pressure.