When your substance either; change color, start to smell, explode, form bubbles, precipitate, and/or get hotter or colder.
        
             
        
        
        
Answer:
Th answer is b. convection.
Explanation:
As the heat rises it cools down and it sinks and as the cold sinks it heats up so then it rises back up.
 
        
             
        
        
        
Answer:
The correct answer is - 18.
Explanation:
The number of hydrogen atoms is indicated by the formula (NH4)2C7H10O2  that has two parts (NH4)2 and C7H10O2 then
Number of hydrogen atoms in (NH4)2 = 4*2= 8
number of H atoms in C7H10O2 = 10
then the total number of atoms = 10+8
= 18.
Thus, the correct answer is = 18 hydrogen atoms.
 
        
             
        
        
        
The question is incomplete:
Complete question is
The most efficient way to determine whether a reaction is an exothermic chemical 
reaction is to use —
A) an oxygen probe
B) a temperature probe
C) a pressure probe
D) a pH probe
...............................................................................................................
Answer:
Reaction is said to be exothermic in nature, if heat is evolved from the system. The resultant product formed is more stable. Since, during exothermic reaction, heat is given out be the system, temperature of system will increase. Hence, temperature is the probe to determine exothermic reaction.
Thus, correct answer is option B) a temperature probe