Chapter 8
Journey Inside the Atom
CBSE Class 9
Science Solutions
Educart Science class Class 9 NCERT Exemplar cover
Question:

Solve this riddle: I am an atom with a mass number of 23 and 11 protons. I am a soft metal and react vigorously with water. Who am I and how many neutrons do I have? You can also create one such riddle. [Pg. No. 152]

Answer: Verified

The atom is sodium (Na).

Reason: Sodium has 11 protons, so its atomic number is 11. It is a soft metal and reacts vigorously with water.

Number of neutrons = Mass number – Number of protons
                                                                      = 23 – 11 = 12

So, the atom is sodium and it has 12 neutrons.

One similar riddle:

I am an atom with a mass number of 35 and 17 protons. I am a greenish-yellow gas and am used to disinfect water. Who am I and how many neutrons do I have?

Answer: Chlorine
               35 – 17 = 18

So, chlorine has 18 neutrons.

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(All Q's of this Chapter solved)
More NCERT Questions
Identify the number of electrons in the outermost shell of the following elements: (A) 612C(B) 919F(C) 1428Si [Pg. No. 152] If a bromine atom is available in the form of, say two isotopes, 3579Br (49.7\%) and 3581Br (50.3\%), calculate the average atomic mass of the bromine atom. [Pg. No. 156] Write the electronic configuration of the elements having atomic numbers 12, 16 and 18. [Pg. No. 152] Two different atoms have 11 protons each, but one has 12 neutrons, and the other has 13 neutrons. How do their atomic numbers and mass numbers compare? Are they the same element or different elements?