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The atomic number (Z) equals the number of protons and, in a neutral atom, the number of electrons. The mass number (A) is the sum of protons and neutrons. For this element, protons = 17, electrons = 17. $Neutrons = Mass Number - Atomic Number = 35 - 17 = 18$

An exothermic reaction is a chemical reaction that releases energy, usually in the form of heat, into the surroundings. This results in a negative change in enthalpy ($-\Delta H$ )

This reaction is a classic example of a reversible reaction, where dinitrogen tetroxide ($N_2O_4$ ) can be converted into nitrogen dioxide ($NO_2$ ), and the nitrogen dioxide can also be converted back into dinitrogen tetroxide. The double arrow ($\rightleftharpoons$ ) indicates that the reaction proceeds in both the forward and reverse directions

The Haber process is the industrial method for synthesizing ammonia from nitrogen and hydrogen gases. It involves reacting nitrogen from the air with hydrogen, which is typically obtained from natural gas or petroleum, under high temperature and pressure in the presence of an iron catalyst.

Boiling is the rapid vaporization of a liquid that occurs when a liquid is heated to its boiling point, and the liquid turns into vapor, forming bubbles within the bulk of the liquid

Boyle's law states that for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume $(P \propto \frac{1}{V})$ . Therefore, if the pressure is tripled, the volume will decrease to one-third of its original value.

In the electrolytic purification of copper, an impure copper block is used as the anode, and a thin strip of pure copper serves as the cathode. When electricity is passed through the copper(II) tetraoxosulphate(VI) electrolyte, copper ions from the anode dissolve and are deposited as pure copper on the cathode

First, the salt is dissolved in water while the sand remains undissolved. Next, the sand is separated by filtration. Finally, the salt is recovered from the water by evaporating the solvent.

Air is a mixture because its components, like nitrogen, oxygen, and argon, are not chemically bonded to each other. They can be separated physically, for example, by fractional distillation of liquid air

A supersaturated solution contains more dissolved solute than a saturated solution at that temperature. It is a metastable state, and the excess solute will often crystallize out if disturbed

The cathode is the negative electrode, where reduction occurs[cite: 205]. In molten NaCl, the ions present are $Na^+ and Cl^-$ . The positive sodium ions ($Na^+$ ) migrate to the cathode and gain electrons to form sodium metal (Na)

Brass is an alloy primarily composed of copper and zinc. Bronze is an alloy of copper and tin. Steel is an alloy of iron and carbon

Insoluble salts are often prepared by a precipitation reaction, where two soluble salts are mixed in an aqueous solution, and the ions combine to form an insoluble product that precipitates out of the solution

According to Le Chatelier's principle, if a change of condition is applied to a system in equilibrium, the system will shift in a direction that counteracts the change. Increasing the concentration of a product will cause the equilibrium to shift to the left (towards the reactants) to consume the excess product and restore equilibrium

The molar mass of FeS is $56 + 32 = 88 g/mol$ . The mass of sulfur in 35.2 g of FeS is calculated as: Mass of $S = (\frac{32}{88}) \times 35.2 g = 12.8 g$ .

Hard water contains dissolved calcium and magnesium salts. These ions react with soap to form an insoluble precipitate called scum, which prevents the soap from lathering and can stain clothes and fixtures. This leads to a waste of soap.

The basicity of an acid is the number of replaceable hydrogen ions per molecule of the acid. Since one molecule of tetraoxosulphate(VI) acid ($H_2SO_4$ ) can furnish two hydrogen ions, its basicity is 2

Halogens are the elements in Group 17 of the periodic table, including fluorine, chlorine, bromine, iodine, and astatine. Chlorine is a representative example

An oxidizing agent is a substance that causes oxidation by accepting electrons. In this reaction, the oxidation number of chlorine changes from 0 in $Cl_2$ to -1 in $KCl$ .This reduction of chlorine means it has gained electrons and is therefore the oxidizing agent

Air is a mixture because its constituent gases, such as nitrogen, oxygen, argon, etc., are not chemically combined and can be separated by physical methods like fractional distillation of liquefied air. The composition of air also varies slightly depending on the location and conditions, which is characteristic of a mixture, not a compound