Question

Place the elements in each set in order of decreasing atomic size.
a. Cl, S, P
b. Ge, Si, C
c. Ba, Ca, Sr
d. S, O, Se

Short answer

Part(a) Order of decreasing atomic size is $\mathrm{P}>\mathrm{S}>\mathrm{Cl}$

Part(b) Order of decreasing atomic size is $\mathrm{Ge}>\mathrm{Si}>\mathrm{C}$

Part(c) Order of decreasing atomic size is $\mathrm{Ba}>\mathrm{Sr}>\mathrm{Ca}$

Part(d) Order of decreasing atomic size is $\mathrm{Se}>\mathrm{S}>\mathrm{O}$

Step-by-step solution

Part(a) Step 1 : Given information

We are given Cl, S, P elements. We have to place the elements in order of decreasing atomic size.

Part(a) Step 2 : Simplify  

Atomic radii drop from left to right across a row and increase from top to bottom down a column, as we know from the periodic table.
The largest atoms are found in the lower left corner of the periodic table, while the smallest are located in the upper right corner, due to these two trends.
As a result, the order will be$\mathrm{P}>\mathrm{S}>\mathrm{Cl}$

Part(b) Step 1 : Given information

We are given Ge, Si, C elements. We have to place the elements in order of decreasing atomic size.

Part(b) Step 2 : Simplify  

Atomic radii drop from left to right across a row and increase from top to bottom down a column, as we know from the periodic table.
The largest atoms are found in the lower left corner of the periodic table, while the smallest are located in the upper right corner, due to these two trends.
As a result, the order will be
$\mathrm{Ge}>\mathrm{Si}>\mathrm{C}$

Part(c) Step 1 : Given information

We are given Ba, Ca, Sr elements. We have to place the elements in order of decreasing atomic size.

Part(c) Step 2 : Simplify  

Atomic radii drop from left to right across a row and increase from top to bottom down a column, as we know from the periodic table.
The largest atoms are found in the lower left corner of the periodic table, while the smallest are located in the upper right corner, due to these two trends.

As a result, the order will be
$\mathrm{Ba}>\mathrm{Sr}>\mathrm{Ca}$

Part(d) Step 1 : Given information

We are given S, O, Se elements. We have to place the elements in order of decreasing atomic size.

Part(d) Step 2 : Simplify  

Atomic radii drop from left to right across a row and increase from top to bottom down a column, as we know from the periodic table.
The largest atoms are found in the lower left corner of the periodic table, while the smallest are located in the upper right corner, due to these two trends.
As a result, the order will be
$\mathrm{Se}>\mathrm{S}>\mathrm{O}$