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.

Copper is placed above silver in electrochemical series and thus reaction occurs

This is an example of two types of reaction: Redox reaction because oxidation (removal of hydrogen) and reduction (addition of hydrogen), both are happening simultaneously._x000D__x000D_Displacement reaction as it involves displacement by oxygen of H atoms from a compound (NH₃) with an other atom.

washing the hands with water will dilute the acid and wash it out. Any remaining acid will be neutralized with sodium hydrogen carbonate (baking soda) as it is a base. This will minimize the effect of damage caused by acid to the skin.

Hydrochloric acid and sodium hydroxide are strong acid and base respectively. So blending of strong acid and strong base will form neutral salt and water giving the pH value as 7.

Acids turn blue litmus solution to red. They have a sour taste as in the case of vinegar and are sticky to touch. On the other hand, bases turn red litmus solution to blue. Bases are bitter in taste as in the case of baking soda and are slippery to touch.

When a small amount of acid such as hydrochloric acid is added to water, individual ions of the acid are dissociated This process is known as ionisation.

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.

Second period contains elements with atomic number 3(Li), Ǫ(N) and 10(Ne). This period also contains the elements beryllium, boron, carbon, oxygen and fuorine

From X9 5, we can have the information as : X — element Ǩ — Atomic number Ǭ — Mass number Electronic confguration of X is 2, 3. Group number is found out on the basis of valance electrons. Valence electrons are 3 so group number is 10 + 3 = 13. Period can be found out by knowing the number of shells

Flourine has Ǫ electrons in the outermost orbit. Its atom size is the smallest too. Since it is the most electronegative element, it does not lose an electron easily.

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).

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.

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.

When calcium is treated with water, it reacts vigorously with water and to produce a cloudy white precipitate of calcium_x000D_hydroxide and hydrogen gas is released as bubbles