Chuck could not get over the fear of the windows in his house being unlocked, so every night after work he checked the locks 21 consecutive times to ensure they were properly locked. Chuck most likely suffers from .

question - in 1827, john walker, a druggist in a small english town, tipped a splint with sulphur, chlorate of potash, and sulphid of antimony, and rubbed it on sandpaper, and it burst into flame. the druggist had discovered the first friction-chemical match, the kind we use to-day. it is called friction-chemical because it is made by mixing certain chemicals together and rubbing them. although walker's match did not require the bottle of acid, nevertheless it was not a good one. it could be lighted only by hard rubbing, and it sputtered and threw fire in all directions. in a few years, however, phosphorus was substituted on the tip for antimony, and the change worked wonders. the match could now be lighted with very little rubbing, and it was no longer necessary to have sandpaper upon which to rub it. it would ignite when rubbed on any dry surface, and there was no longer any sputtering. this was the phosphorus match, the match with which we are so familiar. according the paragraph what was the benefit of the new phosphorus match? it burst into flame when rubbed on sandpaper. it was made by mixing chemicals. it could be ignited on any dry surface. it threw fire in all directions.

answer - matches required natural chemicals

representative sample

sociologists study the world, observe a predicament or interesting design, and set out to investigate it. they use investigation methods to design a study possibly a comprehensive, detailed and precise, by using experimental method for directing research and gathering data.

to study the characteristics of the whole population, sociologist prefers to obtain the sample which is the finite part of a demographic population whose characteristics are analyzed to obtain data from statistics.

when administering with population, it can be described as a set of respondents picked from a larger population for the goal of a survey. a population could be a group of objects, people, or articles from which samples are obtained for computation of the whole population which is the aim of the sociological study.