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Periodic Classification of Elements CBSE Class 10

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Periodic Classification of Elements Topics

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Question 1/20

Q 1. In Mendeleev's periodic table, gold is placed with 

Solution

In Mendeleev's periodic table, gold is placed with alkali metals in Group 1. 

Q 2. The period to which an element belongs is determined from the number of 

Solution

The number of shells determines the period of an element in the modern periodic table. 

Q 3. What is the atomic number of the element belonging to Group 2 Period 2? 

Solution

The element belonging to Group 2 Period 2 is Beryllium with atomic number 4. 

Q 4. Newlands observed that properties of every _____ element are similar to the properties of the first element. 

Solution

Newlands' law states that when the elements are arranged in the increasing order of their atomic masses, the properties of every eighth element are similar to those of the first. 

Q 5. How many elements could fit in Dobereiner’s triads? 

Solution

Dobereiner’s triadsconsist of a group of 3 elements. 

Q 6. What was the name given to eka-silicon after its discovery? 

Solution

Eka-silicon was named germanium after its discovery. 

Q 7. Newlands observed that properties of every _____ element are similar to the properties of the first element. 

Solution

Newlands' law states that when the elements are arranged in the increasing order of their atomic masses, the properties of every eighth element are similar to those of the first. 

Q 8. The unknown element of Mendeleev's periodic table eka-aluminium was later named 

Solution

The unknown element of Mendeleev's periodic table eka-aluminium was later named gallium. 

Q 9. What is the valency of Group17 elements? 

Solution

Group 17 elements have 7 valence electrons. They require 1 electron to complete the octet, so the valency is 1. 

Q 10. Elements separating metals and non-metals are 

Solution

Metalloids separate metals and non-metals. 

Q 11. Dobereiner's law of triads was discarded because 

Solution

The reasons for discarding Dobereiner's law of triads are that it did not cover all the known elements, was based on approximate values and was not fully applicable within thesame family. 

Q 12. Which of the following is the correct order of increasing non-metallic character? 

Solution

On moving from left to right in a period, the non-metallic character increases. So, Li< Be < C < O < F is the correct order. 

Q 13. Which of the following has the smallest size? 

Solution

Al+ has the smallest size, as the size decreases along the period and a cation has a smaller size than its atom. 

Q 14. The halogen which is liquid at room temperature is 

Solution

Bromine is liquid at room temperature. 

Q 15. Which of the following set of elements does not obey Dobereiner's law of triads? 

Solution

S, Te, K does not obey Dobereiner's law of triads as the atomic mass of Te is not equal to the averageof the sum of the atomic masses of the other two elements, S and K. 

Q 16. Mendeleev corrected the atomic mass of__________ element/s. 

Solution

Mendeleev corrected the atomic mass of elements Beryllium, Indium and Uranium. 

Q 17. Elements in the same group have the same 

Solution

Elements in the same group havethe same number of valence electrons 

Q 18. Which of the following elementswill showhigh metallic character? 

Solution

On moving from left to right in a period, the metallic character decreases. So, Na has high metallic character. 

Q 19. What is the valency of the third group in the modern periodic table? 

Solution

The number of valence electrons gives the group number. So, the valency of the third group elements is three. 

Q 20. Group 18 elements are 

Solution

Group 18 elements are noble gases. 

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