Answer: Option (4) is the correct answer.
Explanation:
A mixture is defined as a substance that contains two or more different substance that are physically mixed with each other.
If solute particles are evenly distributed in a solvent then it is known as a homogeneous mixture.
For example, salt dissolved in water is a homogeneous mixture.
If solute particles are unevenly distributed into the solvent then it is known as a heterogeneous mixture.
For example, sand in water is a heterogeneous mixture.
Thus, we can conclude that the statement a mixture must contain at least two different substances, is correct about mixtures.
Answer: The standard state refers to 1 atm and 
.
Explanation:
It is known that a chemical/substance can either be present in a solid, liquid or gaseous state.
So, when the phase of a substance like solid, liquid or gas is present at 1 atmosphere pressure and at a temperature of then it known as standard state of substance.
Thus, we can conclude that standard state refers to 1 atm and .
Q=mc\Delta T
Q= 40.5g x 0.900 J/g degree Celsius x 7.5
Q= 273.4 J.
Even if it is cooled , we use the same temperature as heating it.
