Question

place the following elements in order of decreasing atomic radius. cl, mg, al, ca

Explanation:

Step1: Recall the trend of atomic radius in periodic table

Atomic radius increases down a group (due to addition of new electron shells) and decreases across a period (due to increasing nuclear charge which pulls electrons closer).

Step2: Analyze the positions of elements

• \(Ca\) is in group \(2\) and period \(4\).
• \(Mg\) is in group \(2\) and period \(3\). Since \(Ca\) is below \(Mg\) in the group, \(Ca>Mg\).
• \(Al\) is in group \(13\) and period \(3\). Across period \(3\), \(Mg>Al\) (as nuclear charge increases from \(Mg\) to \(Al\)).
• \(Cl\) is in group \(17\) and period \(3\). Across period \(3\), \(Al > Cl\) (nuclear charge effect).

Combining these: \(Ca>Mg>Al>Cl\)

Answer:

Ca, Mg, Al, Cl