20 points 2 questions can you answer them 1 which of the following reactions is a synthesis reaction? n2 + 3h2 → 2nh3 mgi2 + br2 → mgbr2 + i2 kclo3 → kcl + o2 hcl + naoh → nacl + h2o 2 suppose that the half-life of an element is 1000 years. how many half-lives will it take before one-eighth of the original sample remains? 8 125 12.5 3

The correct options are as follows:
1. A.
A synthesis reaction is a type of reaction in which two or more reactants combine together to form only one product. Synthesis reaction always release energy in form of light and heat, therefore, they are usually exothermic reactions. In the option given in A, nitrogen and nitrogen combine together to form ammonia; this  is a synthesis reaction.
2. D
A radioactive half life refers to the amount of time it will take for half of an original radioactive isotope to decay. 
In the question given above, the half life of the element is 1000. Thus, in 1000 years only half of the original amount will remain. In another 1000 years only 1/4 of the original amount will remain and in another 1000 years only 1/8 of the original amount will remain. Therefore, it will take 3 half lives before 1/8 of the original sample remain.