Specific gravity is the ratio of density of substance and density of water
We know that density of water = 1 g /mL at standard conditions
now as given that the 0.8 Kg of the substance / object is able to displace 500mL of water , it means that
Mass of object = 800g
The volume occupied by 800g of object = 500 mL
Density = mass / volume
Density of object = 800 / 500= 1.6 g / mL
The specific gravity of object = density of object / density of water = 1.6 / 1 = 1.6 (no units)
Answer : The final number of moles of gas that withdrawn from the tank to lower the pressure of the gas must be, 0.301 mol.
Explanation :
As we know that:

At constant volume and temperature of gas, the pressure will be directly proportional to the number of moles of gas.
The relation between pressure and number of moles of gas will be:

where,
= initial pressure of gas = 24.5 atm
= final pressure of gas = 5.30 atm
= initial number of moles of gas = 1.40 moles
= final number of moles of gas = ?
Now put all the given values in the above expression, we get:


Therefore, the final number of moles of gas that withdrawn from the tank to lower the pressure of the gas must be, 0.301 mol.
Boiling water is a physical change, because it is changing state of matter, there is a controllable temperature change, and you can change it back.
Frying the egg white is a chemical change, because there is a change of matter, controllable temperature change, but you CAN'T change it back.
The hockey puck will continue in the same speed in a continues straight line