Atoms and molecules are too small to be weighed. Their masses are expressed as relative masses. On atomic mass scales, by taking the mass of C-12 atom as 12 atomic mass units. The terms used to express relative masses of atoms, molecules and ions are respectively atomic mass, molecular mass, and formula unit mass

Answer the following questions after reading this passage.

(1) Write the value of the ratio,$\frac{AveragemassofOatom}{1/12xMassofC-12atom}$

(2) How many times a molecule of glucose heavier than 1/12th of the mass of a C-12 atom

(3) What is the formula mass of sodium carbonate?

(a) 84 u (b) 106 u (c) 106 g (d) 84 g

(4) Which of the following substances has a molecular mass of 30 u?

(a) Carbon monoxide (b) Carbon dioxide (c) Ammonia (d) Ethane

(1) Average mass of O atom = 16 u

1/12 mass of C-12 atom is equal to 1 amu represented as u.

The value of the ratio, $\frac{AveragemassofOatom}{1/12xMassofC-12atom}$ becomes equal to$\frac{16u}{1u}$

So, the ratio is 16.

(2) Mass of Glucose (C₆H₁₂O₆) = 6 X mass of Carbon(C) atom + 12 X mass of Hydrogen(H)+ 6 X mass of Oxygen(O)

= 6 X 12 + 12 X 1 + 6 X 16

= 180 u

1/12th of the mass of C-12 atom = 1 u

A molecule of glucose is 180 u heavier than 1/12th of the mass of a C-12 atom.

(3) The formula mass of sodium carbonate(Na₂CO₃) is = 2 X mass of Sodium(Na) atom + mass of Carbon(C)+ 3 X mass of Oxygen(O)

= 2 X 23 + 12 + 3 X 16

= 106 u

So, correct option is (b)

(4) The substance has a molecular mass of 30 u is Ethane(C₂H₆)

The molecular mass of Ethane(C₂H₆)= 2 X mass of Carbon(C) + 6 X mass of Hydrogen(H)

= 2 X 12 + 6 X 1

= 24 + 6

= 30 u

So , correct answer is option (d)

The molecular mass of Carbon monoxide(CO)= mass of Carbon(C) + mass of Oxygen(O)

= 12 + 16

= 28 u

Therefore incorrect.

The molecular mass of Carbon dioxide(CO₂)= mass of Carbon(C) + 2 X mass of Oxygen(O)

=12 + 2 X 16

=44 u

Therefore incorrect

The molecular mass of Ammonia(NH₃)= mass of Nitogen(N) + 3 X mass of Hydrogen(H)

= 14 + 3 X 1

=17 u

Therefore incorrect.