Question

Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements inside the front cover as needed:

(a) The isotope of platinum that contains 118 neutrons,

(b) The isotope of krypton with mass number 84,

(c) The isotope of arsenic with mass number 75,

(d) The isotope of magnesium that has an equal number of protons and neutrons.

Answer 1

a)

Isotope of platinum that contains 118 neutrons = 196Pt78

 

Atomic number = Total no of protons

Mass number = Total no of protons + neutrons

Here, atomic number = 78 and mass number = 196,

 

Then, No of neutrons = Mass number - atomic number = 196-78 = 118

 

Therefore, Isotope of platinum that contains 118 neutrons = 196Pt78

 

b)

Isotope of krypton with mass number 84 = 84Kr36

 

Here, atomic number of Kr = 36

Mass number of Kr = 84

 

Therefore,

 

Isotope of krypton with mass number 84 = 84Kr36

 

c)

Isotope of Arsenic with mass number 75 =75As33

 

Here, atomic number of As = 33

Mass number of As = 75

 

Therefore,

 

Isotope of Arsenic with mass number 75 =75As33

 

d) Isotope of Magnesium that has equal no of protons and neutrons = 24Mg12

 

Atomic number = Total no of protons

Mass number = Total no of protons + neutrons

Here, atomic number of Mg = 12

Mass number Mg = 24

 

Hence,

 

No. of neutrons = Mass number - atomic number = 24-12 = 12

 

Then,

No. of protons = No of neutrons = 12

 

Therefore,

Isotope of Magnesium that has equal no of protons and neutrons = 24Mg12

a)

Isotope of platinum that contains 118 neutrons = 196Pt78

 

Atomic number = Total no of protons

Mass number = Total no of protons + neutrons

Here, atomic number = 78 and mass number = 196,