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:
eukaryotic
Explanation:
all human cells—including those found in the brain, the heart, the muscles, and so on—are also eukaryotic.
 
        
             
        
        
        
Answer : The products are Silver sulfide,  and Sodium iodide,
 and Sodium iodide,  .
.
Explanation :
The given balanced chemical reaction is,

From the given balanced reaction, we conclude that the 2 moles of silver iodide react with the 1 mole of sodium sulfide to give product as 1 mole of silver sulfide and 2 moles of sodium iodide.
In a chemical reaction, reactants are represent on the left side of the right-arrow and products are represent on the right side of the right-arrow.
Therefore, in a chemical reaction the products are Silver sulfide and Sodium iodide.