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Science Answer the questions.[Che-3M]

Structure of the Atom · CBSE STD 9 (CBSE - English Medium). 2 questions.

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Answer the questions.[Che-3M]

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Question 13 Marks
Three different atoms of oxygen are represented as:

$^{16}_{\ 8}\text{O},\ ^{17}_{\ 8}\text{O}\text{ and }^{18}_{\ 8}\text{O}$

  1. What do the subscripts (lower figures) and superscripts (upper figures) represent?
  2. What factor is responsible for the change in the superscripts 16, 17 and 18, though the element is the same?
  3. What is the usual name for such atoms of an element?
  4. Give the nuclear composition of $​​^{18}_{\ 8}\text{O}$
Answer
  1. Subscript represents atomic number, whereas superscript represents atomic mass.
  2. Number of neutrons is responsible for the change in superscripts.
  3. Isotope is the usual name for such atoms of an element.
  4. Nuclear composition of 18O8 is

No. of protons = 8

No. of neutrons = 18 - 8 = 10

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Question 23 Marks
From the symbol $^{31}_{15}\text{P},$ state:
  1. Mass number of phosphorus.
  2. Atomic number of phosphorus.
  3. Electron configuration of phosphorus. 
Answer
  1. Mass no. = 31
  2. Atomic no. = 15
  3. Electron configuration: 2, 8, 5.

That is,

$\text{K}\ \ \ \ \ \ \text{L}\ \ \ \ \ \ \text{M}\\2\ \ \ \ \ \ \ 8\ \ \ \ \ \ \ 5$

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