17. which of the following describes a condition in which an individual would not hear an echo?
a. an individual is standing 30 meters in front of the reflecting surface.
b. the reflecting source is approximately 21.5 meters from the individual.
c. an individual is standing in the range of the sound waves coming from the original sound source as well as the reflected waves.
d. a sound wave reaches the ear and the reflected wave reaches the ear less than 0.1 second later.

Electric charge is what ? a. kinetic energy b. radiation c. discovery d. electricity

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.

650.j is the same amount of energy as? 2720cal1550cal650.cal2.72cal