Answer: The space occupied by the gas at 400 torr and 
is 250 mL.
Explanation:
Given: 
= 250 mL, 
= 800 torr, 
, 
= 400 torr, 
Formula used is as follows.
Substitute the values into above formula as follows.
Thus, we can conclude that space occupied by the gas at 400 torr and is 250 mL.
Explanation:
Physical change -
It refers to any change during any process , where there is no new substance is formed , is referred to as a physical change.
Any change in the state of matter is characterised under physical change.
Chemical change -
It refers to any change in a chemical process , where there is formation of any new substance , is referred to as a chemical change .
From the options given in the question,
1. Apple turning brown , on air exposure , is an example of chemical change .
2. The physical state of mercury is liquid , is an example of physical change .
3. phosphorus burns on exposed to air , is an example of chemical change .
4. The gas Neon is colorless at the room temperature , is is an example of physical change .
