If the volume of the object is decreased, measures of its dimensions would also decrease. But keeping the mass constant. Then the buoyant force would also decrease. This can be understood by reasoning why an inflated baloons would float of water but a small metallic sphere of exactly the same mass as the baloon would sink
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how can you reason that bouyant force increases due to increase in density?
bouyant force has nothing to do with the weight of the object.
Bouyant force is equal to the weight of the LIQUID displaced by the object
so, if volume of the object is more (irrespective of its mass), it would displace more liquid and more bouyant force will act on it.
if volume of object is less (mass constant as above), less liquid will be displaced by it, and the bouyant force will be lesser
Buoyant force is directly proportional to the mass if mass is decreased then buoyant force also decreased