Question

re-order each list in the table below, if necessary, so that the atoms or ions in it are listed in order of decreasing size.
atoms or ions\tatoms or ions in order of decreasing size
be⁺, be, li\t□, □, □
br⁻, f⁻, cl⁻\t□, □, □
s, si, cl\t□, □, □

Explanation:

Step1: Analyze first set (Li, Be, Be⁺)

Atomic size: Li > Be; cation size < parent atom, so Be > Be⁺. Order: $\text{Li} > \text{Be} > \text{Be}^+$

Step2: Analyze second set (Br⁻, Cl⁻, F⁻)

For halide ions, size increases down group. Order: $\text{Br}^- > \text{Cl}^- > \text{F}^-$

Step3: Analyze third set (Si, S, Cl)

Across period, size decreases. Order: $\text{Si} > \text{S} > \text{Cl}$

Answer:

atoms or ions	atoms or ions in order of decreasing size
$\text{Br}^-, \text{F}^-, \text{Cl}^-$	$\text{Br}^-, \text{Cl}^-, \text{F}^-$
$\text{S}, \text{Si}, \text{Cl}$	$\text{Si}, \text{S}, \text{Cl}$