Amorphous silica, SiO2, has a density of about 2.2 g/cm3, whereas the density of crystalline quartz, another form of SiO2, is 2.65 g/cm3 . Which of the following statements is the best explanation for the difference in density
(a) Amorphous silica is a network-covalent solid, but quartz is metallic.
(b) Amorphous silica crystallizes in a primitive cubic lattice.
(c) Quartz is harder than amorphous silica.
(d) Quartz must have a larger unit cell than amorphous silica. (e) The atoms in amorphous silica do not pack as efficiently in three dimensions as compared to the atoms in quartz.

Becquerel expected to find ( he developed the photographic plate that had sun-exposed minerals on top of it. becquerel expected to find ( he developed the photographic plate that had been in the closed drawer.

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.

Areaction is first order with respect to reactant x and second order with respect to reactant y. which statement describes the rate law for this reaction?