Question

if the octet rule is not satisfied, which is the correct position for the double bond.
o use lone pair on bromine.
:br=si-s:
o use lone pair on sulfur.
:br-si=s
o use lone pair on fluorine.
:br-si-s:
the octet rule is satisfied.
:br-si-s:

Explanation:

• Fluorine is a highly electronegative element and does not form double bonds easily as it prefers to have a full octet through single - bonds and lone pairs.
• Bromine, although it can expand its octet in some cases, in this context, sulfur is more likely to form a double bond. Sulfur has the ability to use its lone pairs to form double bonds to satisfy the octet rule for the central atom (silicon in this case). When we consider the Lewis structure, if we use the lone pair on sulfur to form a double bond with silicon, it helps in better distributing the electrons to satisfy the octet rule (or at least get closer to a more stable electron - configuration around silicon).

Answer:

Use lone pair on sulfur.