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  Ques 20 : Explain the following terms with one example each.   (a) Corrosion (b) Rancidity Ans 20: (a) Corrosion: Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc. For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.  (b) Rancidity: The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity. For example, the taste and smell of butter changes when kept for long. Rancidity can be avoided by:   1. Storing food in air tight containers 2. Storing food in refrigerators 3. Adding antioxidants 4. Storing food in an environment of nitrogen.  «« Previous question                     Chapter1 Additional Solutions »»

Ques 19 : Oil and fat containing food items are flushed with nitrogen. Why? Ans 19 : Nitrogen is an inert gas and does not easily react with these substances. On the   other hand, oxygen reacts with food substances and makes them rancid. Thus, bags  used in packing food items are flushed with nitrogen gas to remove oxygen inside  t he pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided. «« Previous question              Next question »»

Ques 18 : Why do we apply paint on iron articles? Ans 18 : Iron articles are painted because it prevents them from rusting. When painted,   the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented their presence is essential for rusting to take place.    «« Previous question              Next question »»

Ques 17 : : A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.    Ans 17: ‘X’ is copper (Cu) and the black-coloured compound formed is copper oxide (Cu O).  «« Previous question              Next question »»

                            Electric current The rate of flow of charges through any area of cross-section of a wire is called electric current flowing through it.                   Electric current (I) = q / t.  Its SI unit is ampere (A). The conventional direction of electric current is the direction of motion of positive charge. The current is the same for all cross-sections of a conductor of non-uniform cross-section. Similar to the water flow, charge flows faster where the conductor is smaller in cross-section and slower where the conductor is larger in cross-section, so that charge rate remains unchanged. If a charge q revolves in a circle with frequency f, the equivalent current,                             i = q f  (In a metallic conductor current flows due to motion of free electrons while in electrolytes and ionized gases current flows due to electrons and positive ions.)                           Types of current According to its magnitude and direction electric current is

                            Charge Charge is that property of an object by virtue of which it apply electrostatic force of interaction on other objects. Charges are of two types (i) Positive charge (+ve)  (ii) Negative charge (-ve)  Like charges repel and unlike charges attract each other.               Quantization of Charge Charge on any object can be an integer multiple of a smallest charge (e).                     Q = ± n e where, n = 1, 2, 3,……. and e = 1.6 * 10-19 C.                   Conservation of Charge Charge can neither be created nor be destroyed. but can be transferral from one object to another object. Recently a new particle has been discovered called ‘Quark’. It contains charge ± e / 3, ± 2e / 3. [The protons and neutrons are combination of other entities called quarks, which have charges 1 / 3 e. However, isolated quarks have not been observed, so, quantum of charge is still e. ]         Coulomb’s Law of Electrostatics Electrostatic force of interaction acting betwee

Example 1 : Let A be the set of all students of a boys school. Show that the relation R in A given by R = {(a, b: a is sister of b} is the empty relation and R' = {(a, b: the difference between heights of a and b is less than 3 meters} is the universal relation.  Ans : Since, the school is boys school, no student of the school can be sister of any student of the school. Hence, R = ∅,  showing that R is the empty relation. It is also obvious that the difference between heights of any two students of the school has to less than 3 metres. This shows that R' = A X A is the universal relation.