SCIENCE-10TH CBSE ANSWER KEY

 PERIODIC CLASSIFICATION OF ELEMENTS(8-13)
Question 8:Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Answer: Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons (2) is same in all these three elements. And since chemical properties are due to valence electrons, they show same chemical reactions.

Question 9:Name

(a) three elements that have a single electron in their outermost shells.

(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.
Answer: (a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.

Question 10:(a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer: (a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.
(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.

Question 11:In the Modern Periodic Table, which are the metals among the first ten elements?

Answer: Among the first ten elements, lithium (Li) and beryllium (Be) are metals.

Question 12:By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?

Answer: Since Be lies to the extreme left hand side of the periodic table, Be is the most metallic among the given elements.

Question 13:Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
Answer:(c) The atoms lose their electrons more easily.

(On moving from left to right across the periods of the periodic table, the non-metallic character increases. Hence, the tendency to lose electrons decreases.)

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