CBSE Class X – Science Chemistry Exam (Full Syllabus)

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.

Melting of candle wax on heating is an specimen of physical change no chemical reaction is taking place only the change of state from solid to liquid state.

In Combination and Exothermic reaction, Calcium oxide (CaO), reacts vigorously with water to produce calcium hydroxide (slaked lime) and produces a large amount of heat. Since calcium oxide and water combine to form a single product, calcium hydroxide. So this is a combination reaction.

Clove oil is an olfactory indicator. These the substances which give one type of odour in acidic medium and a diferent odour in basic medium so a visually challenged student favours to use clove oil as an acid-base indicator.

Baking powder is a mixture of sodium hydrogen carbonate and tartaric acid NaHCO₃ + H+ → CO₂ + H₂O + Sodium salt (from tartaric acid) of acid Carbon dioxide (CO₂) produced during reaction can cause bread or cake to rise and makes Baking powder, tartaric acid neutralises the salt and cake does not taste bitter.

Germanium element found a place in the periodic table later in the place of Eka–silicon in Mendeleev’s periodic table.

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).

Pencil lead is formed of graphite. Graphite is an allotropic form of carbon in which each carbon atom is joined to three others, forming layers

Denatured alcohol is the ethyl alcohol which has been made unfit for drinking purpose by adding small amount of poisonous substance like methanol, pyridine, etc.

Ag (silver) would be displaced from the solution of its salts by the other three metals.

The hydrogen gas formed at the initial stage of reaction bubbles on the surface and makes magnesium ribbon lighter. Consequently it does not sink and float on water where as calcium and water are also less violent therefore calcium also floats on water.