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My take: First look is testing concept of matter and matter takes up space (and has weight – not tested).

Observation 1: The balloon expands.

Explanation 1: Air is a matter which takes up space when pumped into the balloon, causing it to expand.

Observsation 2: Some water in the beaker overflowed (or is displaced) into the trough.

Explanation 2: The bigger balloon (with more air inside) takes up more space in the water and caused water to overflow.

I feel the concept of materials and their qualities may not be relevant. Since the cause of the expansion of the balloon is the air (which is matter and takes up space) being pump into it, not directly because it is elastic. Any expert can advise? Appreciate any inputs so I can guide my child too. It is hard for me to guess what setter is looking for in science questions…

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(A) 2 observations are:

(i) The balloon will expand and will rise to the top of the beaker if it is not held in place.

(ii) Water will overflow over the brim of the beaker.

(B) The explanations are:

(i) The balloon expands because it is made of rubber, which is an elastic material.

(ii) The balloon will attempt to rise because air is lighter than water (or has a lower density than water).

(iii) Water will overflow because the air in the balloon occupies space in the beaker.  The volume of water displaced is equal to the volume of air in the balloon.

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