Atomic weight and molecular weight - class-XII

Question 1 Multiple Choice (Single Answer)

Boron has two stable isotopes, $^{10}B (19\%)$ and $^{11}B(81\%)$. Average atomic weight for boron in the periodic table is:

10.8
10.2
11.2
10.0

Question 2 Multiple Choice (Single Answer)

An element $X$ have three isotopes $X^{20}, X^{21}$ and $X^{22}$. The percentage abundance of $X^{20}$ is $90%$ and its average atomic mass of elements is $20.18$. The percentage abundance of $X^{21}$ should be ______________.

$2\%$
$8\%$
$10\%$
$0\%$

Question 3 Multiple Choice (Single Answer)

The fractional abundance of $Cl^{35}$ in a sample of chlorine containing only $Cl^{35}$ (atomic weight $=34.9$) and $Cl^{37}$ (atomic weight $=36.9$) isotopes, is $0.6$. The average mass number of chlorine is _______________.

$35.7$
$35.8$
$18.8$
$35.77$

Question 4 Multiple Choice (Single Answer)

The $O^{18}/O^{16}$ ratio in some meteorites is greater than the used to calculate the average atomic mass of oxygen one earth. The average mass of an atom of oxygen in these meteorites is ______ that of terrestrial oxygen atom?

equal to
greater than
less than
none of these

Question 5 Multiple Choice (Single Answer)

In the atomic weight determination. Dalton suggest the formula of water as $HO$ and the composition of water as hydrogen $=12.5%$ and oxygen $=87.5%$ by weight. What should be the atomic weight of oxygen on $H-$scale, on the basis of this information?

$16$
$8$
$14$
$7$

Question 6 Multiple Choice (Single Answer)

The isotopes of chlorine with mass numbers $35$ and $37$ whose average mass is 35.5 exist in the ratio of:

$1:1$
$3:1$
$3:4$
$3:2$

Question 7 Multiple Choice (Single Answer)

The relative atomic mass of naturally occurring chlorine is not a whole number. What is the reason for this ?

Chlorine atoms can have different number of neutrons
Naturally occurring chlorine cannot be obtained pure
Chlorine is unstable
The mass of the electrons has been included

Question 8 Multiple Choice (Single Answer)

Among the following quantities:
(i) mass number
(ii) average mass of a Carbon atom in amu
(iii) the charge of nucleus in amu and
(iv) mass of a Carbon -12 atom in grams

only (i) is whole number
only (i) and (iii) are whole number
only (i) and (iv) are whole numbers
only (iii) and (iv) are whole numbers

Question 9 Multiple Choice (Single Answer)

What is the approximate molecular mass of dry air containing 78% N$ _2$ and 22% O$ _2$?

48.88
18.88
28.88
38.88

Question 10 Multiple Choice (Single Answer)

What weight of sodium contains the same number of atoms as those in $8$ grams of oxygen?

$10.5 g$
$13.5 g$
$11.5 g$
$14.2 g$

Question 11 Multiple Choice (Single Answer)

What is the atomic mass of sodium?

$22\ g/mol$
$23\ g/mol$
$11\ g/mol$
$20\ g/mol$

Question 12 Multiple Choice (Single Answer)

What is the relative atomic mass of cadmium?

112.411 amu
20.00 amu
21.00 amu
20.43 amu

Question 13 Multiple Choice (Multiple Answers)

Which of the following is/are correct?

One atomic mass unit is a mass unit equal to exactly one -twelfth (1/12th) the mass of one atom of carbon-12.
One atomic mass unit is a mass unit equal to exactly one - sixteenth (1/16th) the mass of one atom of oxygen-16.
The relative atomic mass of the atom of an element is defined as the average mass of the atom, as compared to 1/12h the mass of one carbon-12 atom.
None of the above.

Question 14 Multiple Choice (Single Answer)

Oxygen occurs in nature as a mixture of isotopes $^16O$, $^17O$ and $^18O$ having atomic masses of 15.995 u, 16.999 u and 17.999 u and relative abundance of 99.763%, 0.037%, and 0.200% respectively. What is the average atomic mass of oxygen?

15.999 u
16.999 u
17.999 u
18.999 u

Question 15 Multiple Choice (Single Answer)

For every ,one $^{37}Cl$ isotope there are three $^{35}Cl$ isotopes, in a sample of chlorine. What will be the average atomic mass of chlorine?

35
37
35.5
35.6

Question 16 Multiple Choice (Single Answer)

One gm metal $M^{3+}$ was discharged by the passage of $1.81\times 10^{23}$ electrons. What is the atomic mass of metal?

$8g/mol$
$9g/mol$
$10g/mol$
None of these

Atomic weight and molecular weight - class-XII

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