Which of the following of elements would have all four valence electrons B, Si, As, Te
C, Si, Ge, Sn
O, S, Se, Te
Ga, Ge, As, Se

Explain why scientists use shared characteristics to make cladograms.

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.

Chen drew a diagram to compare the ways in which different organisms obtain nitrogen. which label belongs to the area marked z?