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ICSE CHEMISTRY GIVE REASONS

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Josna Jose
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CHEMISTRY GIVE REASONS CHAPTER 7 METALLURGY Q1. Nitrogen is used to preserve food Due to its inertness. Q2. Group 1 elements are called Alkali metals As they react with water to form their hydroxides which are strong alkalis. Q3. Hydrogen is placed in Group 1 As it has 1 electron. Q4. Most elements do not occur in free state As they are reactive. Q5. Alkali metals are called soft Since they can be cut with a knife. Q6. Alkali metals when freshly cut, they show typical silvery white metallic lustre but soon they turn dull [tarnish] Because of their reaction with air. Q7. Elements of Group 2 are called Alkali Earth metals Because their oxides occur in the earth s crust and their hydroxides are alkalies. Q8. Metals form +ve ion [cations] Because of loss of electrons. Q9. Non-metals form ve ions Because of gain of electrons which have a ve charge. Q10. Potassium is kept at the top of the activity series of metals. Because it is the most reactive metal; the arrangement of metals in the activity series is in the decreasing order of their reactivity. Q11. Hydrogen, though a non-metal has been included in the activity series Because it can form a positive ion. It would occupy the position based on the formation of the positive ion. Q12. The reaction of dilute acids with lead is very slow. Because the salts formed are sparingly soluble in dilute acids. During the reaction, the chloride or sulphate gets coated on the metal and prevents the reaction to proceed further. Q13. Oxides of K, Na, Ca, Mg, Al cannot be reduced by heating. As they are stable to heat and so can be reduced only by electrolysis. Q14. Reactive metals like sodium and potassium are kept in kerosene oil

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