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Page No 85: - Chapter 5 - Periodic Classification Of Elements - Ncert Solutions class 10 - Science


Question 1:

Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:

K, C, Al, Si, Ba.

Answer:

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 will be Al2O3.

Si is in group 4. Therefore, the oxide will be SiO2.

Ba is in group 2. Therefore, the oxide will be BaO.

Question 2:

Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)

Answer:

Scandium and germanium

 Question 3:

What were the criteria used by Mendeleev in creating his Periodic Table?

Answer:

Mendeleev’s periodic table was based on the observation that the properties of elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals.

Question 4:

Why do you think the noble gases are placed in a separate group?

Answer:

Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separate group.