Which of the following accurately describes properties of valence? a. nonmetallic elements tend to have a positive valence and tend to be electron borrowers. b. metals tend to have a negative valence and tend to be electron borrowers. c. the greater the number of electrons an atom has to borrow or to lend, the greater the activity of the atom. d. the smaller the number of electrons an atom has to borrow or to lend, the greater the activity of the atom

The scheme below is from a series of reactions that are part of a synthesis of vitamin a. answer the following questions with reference to this scheme. (i) what is "reagent a"? (ii) draw a step-by-step mechanism which explains the formation of compound c from compound b (iii) which reagents would you use to form compound e from compounds c and d (reagents b and c)? for each reagent suggested above in (ii) explain the role of the reagent in the reaction to (iv) form compound e. you may wish to do this by drawing a mechanism. 1. addition of reagent a но reagent a 2. н,о" thо oh нон-с compound a. compound b. compound c .ch-оh 1. reagent b "сно 2. reagent c сh oh compound e. compound d.