Explanation:
A change that does not cause any change in chemical composition of a substance is known as a physical change.
For example, mass, density, volume etc are all physical changes.
On the other hand, a change that brings change in chemical composition of a substance is known as chemical change.
For example, combustion, toxicity, reactivity etc are all chemical changes.
Hence, following statements are identified as chemical or physical changes as follows.
(a) Oxygen gas supports combustion : Chemical change
(b) Fertilizers help to increase agricultural production : Chemical change
(c) Water boils below
on top of a mountain : Physical change
(d) Lead is denser than aluminum : Physical change
(e) Uranium is a radioactive element : Chemical change
Their is 2 valence electrons

☃️ Chemical formulae ➝ 
How to find?
For solving this question, We need to know how to find moles of solution or any substance if a certain weight is given.

Solution:
❍ Molecular weight of 
= 2 × 126.90
= 253.80
= 254 (approx.)
❍ Given weight: 12.7
Then, no. of moles,
⇛ No. of moles = 12.7 / 254
⇛ No. of moles = 0.05 moles
⚘ No. of moles of Iodine molecule in the given weight = <u>0.05</u><u> </u><u>moles </u>
<u>━━━━━━━━━━━━━━━━━━━━</u>
<h3>
Answer:</h3>
= 19.712 kJoules
<h3>
Explanation:</h3>
- Heat of vaporization refers to the amount of heat required to change a unit mass of a substance from liquid to gaseous state without change in temperature.
To calculate the amount of heat, we use,
Amount of heat = Mass × Heat of vaporization
Q = m×Lv
Given;
Mass of liquid Zinc = 11.2 g
Lv of liquid Zinc = 1.76 kJ/g
Therefore;
Q = 11.2 g × 1.76 kJ/g
= 19.712 kJ
Thus, the amount of heat needed to boil 11.2 g of zinc is 19.712 kilo-joules.
Answer:
1) mass and volume
2) float.
3) Sink
4) Apples
5) Cannonball
Explanation:
1) Density is based on the mass and volume of a material.
2) A material or an object with low density than water or liquid tends to float.
3) A material or an object with high density than water or liquid tends to sink.
4) The apples in the water have less density as they are floating in the water.
5) The cannonball is more dense than the ocean water and the ball sink in the less density water.