Structure of Atom Test

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Structure of Atom Test - 28

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Weekly Quiz Competition

Question 1
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Find number of protons and neutrons for (a),(b) and (c) respectively.
(a) $$\begin{matrix}35\\ 17\end{matrix} Cl$$(b) $$\begin{matrix}12\\ 6\end{matrix} C$$(c) $$\begin{matrix}81\\ 35\end{matrix} Br$$.

A
$$n_p$$= 17,6,35

$$n_n$$= 18,6,46

B
$$n_p$$=16,6,35

$$n_n$$= 18,6,46

C
$$n_p$$=17,6,35

$$n_n$$= 18,6,45

D
$$n_p$$=16,6,35

$$n_n$$= 18,6,45

Solution

For an element $$X$$, the mass number and atomic no. are represented as; $$X^{mass \ no}_{atomic \ no}$$
Number of neutrons + number of protons= Atomic mass number.
Atomic number = number of protons = number of electrons
Therefore for $$Cl$$: $$n_{p}$$ $$= 17$$ & $$n_{n}$$ $$= 35-17 = 18$$
For $$C$$ : $$n_{p}$$ $$= 6$$ & $$ n_{n}$$ $$= 12-6 = 6$$
For $$Br$$: $$n_{p}$$ $$= 35$$ & $$n_{n}$$ $$= 81-35 = 46$$
Question 2
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Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order.
(i) Rutherfords atomic model
(ii) Thomsons atomic model
(iii) Bohr's atomic model

A
(i), (ii) and (iii)

B
(ii), (iii) and (i)

C
(ii), (i) and (iii)

D
(iii), (ii) and (i)

Solution

Sir J J Thomson in 1897 studied the characteristics of cathode rays and discovered protons.

Lord Rutherford in 1911 studied the atomic model and discovered the atomic nucleus.

Bohr later explained the stability of the atom which was not explained by the others in their atomic theory.
Question 3
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How many lines does a spectrum contain in an electronic transition from $$n =1 \:to \:n = 5$$ in hydrogen atom?

A
$$10$$

B
$$8$$

C
$$1$$

D
$$5$$

Solution

The no. of spectral lines produced in a spectrum = $$\dfrac{{(n_{2}-n_{1})(n_{2}-n_{1}+1)}}{2}$$.
Given that $$n_{2}$$ = 5 and $$n_{1}$$ = 1; the no. of spectral lines = $$\dfrac{4\times 5}{2}$$
$$= 10.$$
Question 4
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The ratio of the radii of hydrogen atom and its nucleus is$$~ 10^5.$$ Assuming the atom and the nucleus to be spherical, if atom is represented by planet earth $$R_e = 6.4 \times10^6 m$$, estimate the size of the nucleus(radius).

A
56 m

B
60 m

C
64 m

D
68 m

Solution

$$\frac {R_e}{r_n} = 10^5$$
If the atom is represented by the planet earth $$(R_e = 6.4 \times 10^6 m)$$ then the radius of the nucleus would be $$\displaystyle r_n = \frac {R_e}{10^5}$$
$$\displaystyle r_n = \frac {6.4 \times 10^6 m}{10^5}$$
$$6.4 \times 10 m$$
$$= 64 m.$$
Question 5
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The electronic configuration of element with atomic no. $$14$$ is:

A
$$(2, 6, 6)$$

B
$$(4, 6, 4)$$

C
$$(2, 4, 8)$$

D
$$(2, 8, 4)$$

Solution

Electronic configuration of element with atomic number with $$14$$ is $$2, 8, 4$$
Question 6
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Calculate the mass number of atoms $$X, Y$$ and $$Z$$?

A
5, 11, 18

B
10, 18, 31

C
11, 18, 31

D
11, 19, 30

Solution

Atomic mass number = Total number of protons + Total number of neutrons
For $$\mathrm{X}$$, Atomic mass number = $$\mathrm{6+5=11}$$
For $$\mathrm{Y}$$, Atomic mass number= $$\mathrm{8+10=18}$$
For $$\mathrm{Z}$$, Atomic mass number= $$\mathrm{15+16=31}$$
Hence, option $$\mathrm{C}$$ is the correct answer.
Question 7
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In which of the following, Aufbau principle is violated?

A

B

C

D

Solution

According to Aufbau principle, orbitas are filled in order of increasing energy levels. Therefore one with minimum energy is filled first and then electron enters the next orbital. In (D), s-orbital (low energy) is not fully filled and electrons enter in the p- orbital (higher energy), thus violating the aufbau principle.
Question 8
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The number of electrons, protons and neutrons in an atom whose atomic number is 11 and mass number 23 will be:

A
$$11, 11, 12$$

B
$$11, 12, 11$$

C
$$12, 11, 11$$

D
$$23, 11, 23$$

Solution

Mass number $$ = $$ 23 and atomic number $$=$$ 11.

Atomic number $$=$$ Number of electrons $$= $$Number of protons $$= 11$$.

Number of neutrons $$=$$ Mass number $$-$$ atomic number $$= (23-11) = 12$$.

Hence, option A is correct.
Question 9
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In an atom, the differentiating electron enters into 7s sub shell. The number of incomplete shells in the atom could be:

A
$$1$$

B
$$2$$

C
$$3$$

D
$$0$$

Solution

According to Aufbau's Principle, when the differentiating electron enters into the 7s subshell, there will be three incomplete shells (7, 6, 5).
Question 10
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For manganese atom, assuming that Hund's rule is not valid for $$l=2\:sub shell,$$ predict the unpaired electrons and electron pairs in that sub shell of atom.

A
$$5, 1$$

B
$$5, 0$$

C
$$1, 2$$

D
$$1, 3$$