Answer:
A. Compounds
Explanation:
Firstly, don't let the word "pure" confuse you; this is pretty much irrelevant to the question.
The key to answering this question lies in "substance" and "more than one type of element chemically bonded."
Something you ought to memorize is that a substance is either an element or compound. Therefore, you can eliminate choices B./C. 
Next, use the part of the definition that says "more than one type of element chemically bonded" to conclude that it's a compound. Not only is this the definition of a compound, but the fact that is says <em>more than one type of element</em> should automatically tell you that it is different from just a regular element (Choice D.).
 
        
             
        
        
        
Answer:
The final temperature of the solution is 44.8 °C
Explanation:
assuming no heat loss to the surroundings, all the heat of solution (due to the dissolving process) is absorbed by the same solution and therefore:
Q dis + Q sol = 0
Using tables , can be found that the heat of solution of CaCl2 at 25°C (≈24.7 °C)  is q dis= -83.3 KJ/mol . And the molecular weight is 
M = 1*40 g/mol + 2* 35.45 g/mol = 110.9 g/mol
Q dis = q dis * n  = q dis * m/M =  -83.3 KJ/mol * 13.1 g/110.9 gr/mol = -9.84 KJ
Qdis= -9.84 KJ
Also Qsol = ms * Cs * (T - Ti) 
therefore
ms * Cs * (T - Ti) + Qdis = 0
T=  Ti - Qdis * (ms * Cs )^-1   =24.7 °C - (-9.84 KJ/mol)/[(104 g + 13.1 g)* 4.18 J/g°C] *1000 J/KJ
T= 44.8 °C
 
        
             
        
        
        
Answer:
Oxygen and sulfur
Explanation:
Alloys consist of metals fused together sometimes with additional components, such as carbon, to prevent metals from corrosion.
Oxygen and sulfur are two compounds consisting of non-metal atoms, O and S. Combining oxygen with sulfur would actually produce sulfur dioxide, a gas, in contrast to a metallic substance that is fused with some other metal or carbon.
That's the reason why combination of sulfur and oxygen wouldn't produce an alloy: it would produce a gas.