5. B air is a mixture of many elements, but is not a chemically fused.
6. B Beef stew, composition varies throughout.
7. A. They can be chemically separated into their component elements, but they are all homogenous, and as such, have constant composition, which differs from the components properties, as the components must undergo a chemical change to become compounds.
 
        
             
        
        
        
Answer: 
The statements which are true among these are: (a),(b) and (c) because,
(a) The simplest organic compounds which contains only carbon and hydrogen atoms are called hydrocarbons.
(b) The IUPAC naming of organic compounds have some rules for the naming of compounds, which consists of 
- Finding the longest chain present in the compound called parent chain.
- A prefix for any substituent attach to the parent chain.
And lastly a suffix for the type of bond that molecule have.
(c) Isomers are the compound which same same molecular formula but different arrangement of molecules, due to this different arrangement they have different physical and chemical properties.
 
        
             
        
        
        
Answer
A. It changes the rate, R
Explanation
When we change the concentration of the reactants in a chemical reaction, it affects the rate of reaction that happens in the process. Typically, the rate of reaction will decrease with time if the concentration of the reactants decreases because the reactants will be converted to products. Similarly, the rate of reaction will increase when the concentration of reactants are increased.
 
        
             
        
        
        
Answer:
Giá trị xà phòng hóa hoặc số xà phòng hóa (SV hoặc SN) biểu thị số miligam kali hydroxit (KOH) hoặc natri hydroxit (NaOH)