Choose the incorrect trend in the atomic radii (r) of the elements.
- rRb < rCs
- rAt < rCs
- rBr < rK
- rMg < rAl
Answer
(4) rMg < rAl
Solution
(1) Rb and Cs are in group 1; radius increases down the group rRb < rCs. Correct trend.
(2) At (period 6, group 17) and Cs (period 6, group 1): radius decreases across a period rAt < rCs. Correct trend.
(3) Br and K are in period 4; K is at the left end rBr < rK. Correct trend.
(4) Mg and Al are in period 3; Al lies to the right of Mg, so rAl (143 pm) < rMg (160 pm). The given trend rMg < rAl is incorrect.
Answer: (4)