NCERT
- Name (b) two elements that have two electrons in their outermost shells. Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells. 1
- Name (a) three elements that have a single electron in their outermost shells. Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells. 1
- Name two elements you would expect to show chemical reactions similar to magnesium. Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence ele... 1
- How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table? Various anomalies of Mendeleev’s Periodic Table removed as follows in the Modern Periodic Table: → Elements are arranged in the increasing o... 2
- Why do you think the noble gases are placed in a separate group? Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separ... 1
- What were the criteria used by Mendeleev in creating his Periodic Table? Mendeleev used atomic mass of the elements as the unique criteria of the elements. He proposed that the chemical properties of elements are... 2
- Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? Scandium and germanium. 2
- Use Mendeleev's Periodic Table to predict the formulae for the oxides of the following elements: K, C, Al, Si, Ba. K is in group 1. Therefore, the oxide will be K₂O. C is in group 4. Therefore, the oxide will be CO₂. Al is in group 3. Therefore, the oxide... 1
- What were the limitations of Newlands' Law of Octaves? Limitations of Newlands' law of octaves: → It was not applicable throughout the arrangements. It was applicable up to calcium only. The prop... 1
- What were the limitations of Dobereiner's classification? Limitation of Dobereiner's classification: All known elements could not be classified into groups of triads on the basis of their properties... 1
- Did Dobereiner's triads also exist in the columns of Newlands' Octaves? Compare and find out. Yes, Dobereiner's triads also exist in the columns of Newlands' Octaves. One such column is Li, K, Na. 1
- Explain the mechanism of the cleaning action of soaps. The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When so... 1
- Give a test that can be used to differentiate chemically between butter and cooking oil. Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand, oil has unsaturated fats. That is why it can be hyd... 2
- Which of the following hydrocarbons undergo addition reactions: C2, H6, C3H8, C3H6, C2H2 and CH4. Unsaturated hydrocarbons undergo addition reactions. Being unsaturated hydrocarbons, C₃H₆ and C₂H₂ undergo addition reactions. 1
- What is hydrogenation? What is its industrial application? Hydrogenation is the chemical reaction between hydrogen and other compounds in the presence of catalyst. Hydrogenation is used mainly to red... 2
- What change will you observe if you test soap with litmus paper (red and blue)? Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus will remain blue. 1
- Explain the formation of scum when hard water is treated with soap. Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitat... 1
- Why are carbon and its compounds used as fuels for most applications? Carbon and its compounds give large amount of heat on combustion due to high percentage of carbon and hydrogen. Carbon compounds used as fue... 1
- Why does micelle formation take place when soap is added to water? Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water and clothes are put in th... 2
- How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties? Ethanol and Ethanoic acid be differentiated on the basis of their following properties: → Ethanol is a liquid at room temperature with a ple... 1
- What is a homologous series? Explain with an example. A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group. For e... 1
- Draw the electron dot structures for (a) ethanoic acid. (b) H2S. (c) propanone. (d) F2. (a) ethanoic acid. (b) H₂S. (c) propanone. https://lh3.googleusercontent.com/-f094hG0mOdM/YbC7aIlXOCI/AAAAAAAAC48/OTqTboXC68IMajlrBd2YhgRHex... 2
- Explain the nature of the covalent bond using the bond formation in CH3Cl. The structure of CH₃Cl is given below: Carbon has four valence electrons. It shares 1 electron each with 3 hydrogen atoms and 1 electron wit... 1
- While cooking, if the bottom of the vessel is getting blackened on the outside, it means that Correct option is b) the fuel is not burning completely. 2