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Today we will see the rest of class 10th scientific reasons.

1. Sodium is always kept in kerosene. (highly active, density, )
Ans:- 
•  At normal / room temperature sodium (Na) metal combines very strongly with oxygen O2. 
• Sodium metal reacts with Oxygen in the air, water vapor, and carbon dioxide. 
•  The density of Sodium is more than kerosene, so it sinks in it. Sodium does not react with kerosene. So sodium is always kept in kerosene.
2. Lemon or tamarind are used for cleaning copper vessels that turn greenish.
(Black copper oxide, green copper carbonate, acid)
Ans:-
•  Copper gets oxidized in the air to form black copper oxide. Copper oxide reacts slowly with carbon dioxide in the air and creates a green coating. This green substance is called copper carbonate.
•  Lemon contains citric acid and tamarind contains tartaric acid. This acid dissolves the green coating of basic copper carbonate and makes copper vessels shiny again.
• Therefore Lemon or tamarind are used for cleaning copper vessels that turn greenish.

* Anodes need to be replaced from time to time during the electrolysis of alumina.
( Oxygen, erode carbon electrode)
• Ans:-1. In the process of electrolysis of alumina the Oxygen (O2) gas liberated at the carbon anode reacts with graphite (C) rods and forms carbon dioxide(CO2).
• 2. During electrolysis of alumina graphite rods continuously erode because they get oxidized.
• C +O2 —> CO2
Hence Anodes need to be replaced from time to time during the electrolysis of alumina.

* Calcium floats on water during the reaction with water.
( less vigorous reaction, insufficient heat, hydrogen gas sticks to calcium)
• Ans:- 1. Calcium metal reacts with water less vigorously therefore the heat evolved is not sufficient for hydrogen to catch fire.
• 2. The bubbles of hydrogen gas stick to the surface of sodium metal, so calcium floats on water.
* Generally the ionic compounds have high melting points.
( strong electrostatic force, hard and solid )
Ans:- 
• 1. Ionic compounds are formed by a strong electrostatic force of attraction between oppositely charged ions. Therefore ionic compounds are hard and they exist in a solid state.
• 2. Large energy is required to overcome the intermolecular force of attraction of ionic compounds.
• Hence generally the ionic compounds have high melting points.
* Carbon atoms are capable of forming an unlimited number of compounds.
( Tetravalent, Catenation, single, double or triple bond, Catenation)
Ans:- 
•  Tetravalent tendency:-
• Carbon atoms can bond with four other carbon atoms or atoms of other monovalent elements.
• Catenation:-
• Carbon atoms can share their valence electrons to form single, double, and triple bonds.
•  Multiple bonding:-
• Carbon atoms can form multiple bonds with themselves and other atoms, such as nitrogen, oxygen, or hydrogen.
•  Carbon atoms can also form straight chains, branched chains(isobutane), and rings [benzene (C6H6)].
• Hence Carbon atoms are capable of forming an unlimited number of compounds.

* Geostationary satellites are not useful for the study of polar regions. Or
Why are geostationary satellites not useful for studies of polar regions.
( position, same speed, equator)
Ans:-
• Geostationary satellites orbit the Earth at the equator and rotate at the same speed as the Earth.
• Geostationary satellites remain fixed in the same position respective to the Earth’s surface
• They do not fly about the polar regions.
Hence Geostationary satellites are not useful for the study of polar regions.

* Ethylene is an unsaturated hydrocarbon.
(Definition, double bond.)
Ans:-
• 1. Definition:- Those hydrocarbons contain carbon carbon double or triple bonds they are called unsaturated hydrocarbons.
• 2. The ethylene molecule contains a carbon double bond.
• 3. This means the valencies of the two carbon atoms are not fully satisfied by a single covalent bond.
Hence ethylene is an unsaturated hydrocarbon.

🎷 Today let’s look at one more question type. In this question type, there is no need to write an explanation of the answer.
Q.1 B sets 
Q.1 B sets contents questions of the type “write the name/ molecular formula/ electronic configuration.

This question, Question No. 1(b), is carried for one mark.

• * Alkali metal from the second period            
Answer:- Lithium (Li)

• * Halogens in the 3rd period.            
Answer:- Chlorine ( Cl )
• * Horizontal rows in the modern periodic table.            
Answer:- periods.

• * The element with electronic configuration 2,8,7            
Answer:- Chlorine (Cl)

• * The elements with stable electronic configuration.

Answer:- 1. Helium (He), Neon (Ne), Argon( Ar), krypton (Kr), xenon(Xe).
• Right two names of inert gas/ noble gas or 18 group elements.

Answer:- 1. Helium (He), Neon (Ne), Argon( Ar), krypton (Kr), xenon(Xe).

• * Three elements have 7 electrons in their outermost shell.
Right names of three elements belonging to the Halogen group.
Ans:- 1. Fluorine (F)
2. Chlorine (Cl)
3. Bromine(Br)
4. Iodine(I)

• * Two elements have a single electron in their outermost shell.
Or
• Write to names of alkali metals.
Ans:- 1. Lithium (Li)
2. sodium (Na)
3. potassium ( K)

• * An alkali metal in the period 2.
Ans:- 1. Lithium (Li)

• * An alkaline earth metal in the period 3.
Ans:- Magnesium (Mg)

• * Three nonmetallic elements in period 2.
Ans:- 1. Nitrogen (N) 
2. Oxygen (O)
🥁 Write the name and symbol of the element from the description
• * The atom has the smallest atomic mass.
Ans:-Hydrogen (H)
• * The atom has the smallest size.
Ans:- Helium (He)  
Many people would think that the answer is hydrogen but it is not. Helium is the smallest 🥁 element in the periodic table. Helium has a size of 31 pm while hydrogen has a size of 53 pm. 🎺🥁🎇
• * The most electronegative atom.
Ans:-fluorine (F) 
• * The noble gas with the smallest atomic nucleus.        
Ans:- Helium (He)
• * The most reactive nonmetal         
Ans:- Fluorine (F)
• * The product forms in the thermal decomposition of sugar.        
Ans:- Carbon (C)
• * The gas evolved when sodium metal reacted with ethanol.        
Ans:- Hydrogen (H)
• * The precipitate formed when barium sulphide BaS reacted with zinc sulphate ZnSO4.        
Ans:- Barium sulphate (BaSO4)
• * The reducing agent used for the reduction of copper oxide.        
Ans:- Hydrogen (H)
• * The oxidizing agent used to oxidize ferrous sulphate.        
Ans:- potasium paramagnet (KMnO4)
• * Name the first artificial satellite sent by Russia into space.        
Ans:- Sputnik
• * The number of double bonds in benzene.        
Ans:- Three
• * The main component of natural gas.        
Ans:- methane (CH4)
• * Nomenclature system based on the structure of the compounds and it was accepted all over the world.        
Ans:- international union of pure and applied chemistry (IUPAC)
• * The device used for grinding an ore.        
Ans:- grinding mill
• * The process of heating the carbonate ore to a high temperature in limited air.        
Ans:- calcination
• * The process of heating the sulphide ore to a high temperature over the air.        
Ans:- roasting
• * Two Highly reactive metals.        
Ans:- 1. potassium                     
2. sodium
• * A common ore of aluminum.            
Ans:- Bauxite { Al2O3,H2O}
• * Compounds that are added to lower the fusion temperature of alumina.        
Ans:- cryolite and fluorspar
• * An alloy of copper and zinc.            
Ans:- brass
• *A metal that forms an amphoteric oxide.            
Ans:- aluminum (and zinc)
• * A metal that does not react with cold water but reacts with steam.
Ans: 1. Aluminium         
2. Iron        
3. zinc
• * The lens that forms a real image or virtual image depending on the position of the object.        
Ans:- A convex lens
• * Name the lens which produces magnification always less than 1.            
Ans:- A concave lens
• * Constituents of the alloy used to make a fuse wire.        
Ans:- Lead (Pb) & tin (Sn)

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