CBSE Class X – Science Chemistry Exam (Full Syllabus)

Inert gases like helium or nitrogen both can be used for the storage of fresh sample of oil for a long time, as they do not react with most elements, including oxygen

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid. So formed remains in the solution.

Potassium iodide on reacting with lead nitrate gives yellow precipitate of lead iodide.KI + Pb(NO3)2 → PbI2 + KNO3

When the pH of an aqueous solution is higher, its acidic properties are weak. Thus, it is a base. When the pH an aqueous solution is lower, its basic properties are weak. Thus, it is an acid.

Elements having the same number of valence electrons belong to the Same group.

The element with electronic confguration 2, 8 has octet confguration, so it must be an inert gas, i.e., neon, which is placed in group 18.

The atomic number of F, O and N are Ǭ, 8 and Ǫ respectively and they belong to the same period i.e. 2nd period. The atomic radius decreases in moving from left to right along a period.

Eka-aluminum (later identified as gallium) has a valency of 3. Hence, the oxide would be of the molecular formula E₂O₃. Other options have a different valency of E.

Only 0.03% of atmospheric air contains carbon in the form of carbon dioxide. The natural concentration of  carbon monoxide  in  the air  is around 0.2 parts per million (ppm).

It is the element which possess tetravalent property and thus form covalent compound.

Carbon always forms covalent compounds by sharing its electrons with other at atoms.The two electrons shared by the atoms are attracted to the nucleus of both the atoms.

A cation is formed by loss electrons from the atom of an element which acquires positive charge due to the presence of greater number of protons as compared to that of electrons.

Metals generally do not show dullness. Metals such as gold and silver are usually shiny comparatively than dull.

Na (sodium) and Ca (calcium) react vigorously with water. Mg (magnesium) respond with water less vigorously than calcium and sodium. Fe (iron), on the other hand, does not react with cold as well as hot water instantly.

Aqua-regia is the mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua-regia, being a strong acid, dissolves gold.