Question

One 'U' stands for

a.An atom of carbon (C-12)
b.1/12th of mass of carbon atom (C-12)
c.1/12th of hydrogen atom
d.All of the above​

Answer 1

One 'u' stands for 1/12th of the mass of carbon atom (C-12) [Option.b]

Some Extra Information:-

• The atomic masses of all other elements

are determined by comparing the mass

of their atom with the mass of a

carbon-12 atom.

• 1u = 1/12th the mass of C-12 atom.

• The atomic mass of an element

indicates the number of times one atom

of the element is heavier than 1/12 of a

Carbon-12 atom.

•The present standard for the atomic

masses is carbon-12 atom, which has

been assigned an atomic mass of

exactly 12u.

• Mass of a C-12 atom = 1.9926×10⁻²³ g

Thus, absolute mass of the atomic mass unit (u) :-

= 1.9926×10⁻²³/12

= 1.6605×10⁻²⁴ g

Thus:-

=> 1 u = 1.6605×10⁻²⁴ g

Answer 2

b) 1/12th of mass of carbon atom (C - 12)

Formerly, scientists took 1 u as 1/16th of oxygen. This is because,

• Oxygen gave most of the relative masses of other elements as whole numbers.
• It reacted with many elements to form compounds.

But, later IUPAC declared 1 u (amu) as 1/12th of carbon 12 isotope.