CBSE Class X – Science Chemistry Exam (Full Syllabus)

Both these processes produce a cooling efect rather than heating. Dry ice absorbs heat from the environment to convert into gas. This feature makes it a good refrigerant. Processes of dilution of sulphuric acid and condensation of water vapours produce a large amount of heat. There fore these are exothermic processes.

A physical change involves only change in physical state whereas a chemical change results in the formation of new substances. Boiling of water, melting of ice and dissolution of salt are physical changes as no new products are formed.

Decomposition reaction can be defined as the reaction which involves decomposition of one compound to more than one substance. Endothermic reactions require heat energy to form products.

In standard conditions, hydrogen and oxygen exist in a gaseous state, whereas water exists in a liquid state.

Calcium phosphate Ca₃(PO₄)₂  is a basic salt, as it is formed by the combination of a weak acid (phosphoric acid) and a slightly stronger base (calcium hydroxide)

On a pH scale acidity ranges from 1 to 7 and it increases by moving down from 7 to 1 while basicity ranges from 7 to 14 which increases by moving up from 7 to 14.

When an acid responds with a base, a neutral salt is formed by the neutralisation process. As the neutralisation process is an exothermic reaction, the temperature of the solution become greater.

The elements boron (B), silicon (Si) and germanium (Ge) exhibit intermediate properties of metals and non-metals, therefore, they are called as metalloids

As we move down in a group, the metallic nature of elements increases.  Be, Mg and Ca are present in the same group (group 2 of the modern periodic table).

Aluminum is more reactive than iron, it displaces iron from ferrous sulphate solution. The green colour of ferrous sulphate solution slowly changes to brown as iron is formed.

Nitric acid (HNO₃) is a strong oxidizing agent, so it does not give hydrogen gas on reacting with metals (except Mn and Mg).

At room temperature, mercury (Hg) is the only metal found in liquid state.

Element X is Sodium Aluminate. Al₂O₃ is chemically called aluminum oxide or we can say it is a metal oxide. Aluminum oxide shows basic as well as acidic behavior. Such metal oxides are called amphoteric oxides.