The correct option is A 1.0M KOH
From elevation in boiling point,
ΔTb=i×Kb×m
where,
△Tb is the elevation in boiling point.
Kb is molal elevation constant.
m is molality of solution.
i is van't Hoff factor
From the equation we can say lower the value of i×m lower will be the boiling point elevation.
Considering all the compounds exhibit 100% dissociation,
KOH⇒i×m=2×1=1(NH4)2SO4⇒i×m=3×1=3K2CO3⇒i×m=3×1=3K2SO4⇒i×m=3×1=3
Since, i×m is lower for KOH, the boiling point will be lower for 1 M KOH