If you wanted to find an element that would react similarly to chlorine (CI),
where would you look and why?

 Fluorine (F) and chlorine (Cl) are two good choices.  See reasoning below.

Explanation:  Mendeleev arranged the elements in the periodic table in a manner that each group, or vertical column, contained elements that exhibited similar chemical properities.  He even reserved spaces for undiscovered elements when none of the known elements had properties similar to those above or below the known elements in a group.  An interesting event illustrates this property.  In December 2010, NASA announced an important new discovery that was to be broadcast on live TV, creating much speculation (e.g., UFO's are real and we'll see the aliens sequestered at Roswell!!!  I knew it.).  

The actual announcement:

"Dec. 2, 2010:  NASA-supported researchers have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism, which lives in California's Mono Lake, substitutes arsenic for phosphorus in the backbone of its DNA and other cellular components."

A look at the periodic table shows arsenic just below phosphorus, in the same group.   This was an unexpected find, but it might have been predicted with an understanding of how the elements are organized.  

Side note:  look how close silicon is to carbon.  Can there be a life form whose being is made up of silicon instead of carbon?  Sure . . . why not?  Maybe not on Earth, but . . . wait . . . did that marble statue just wink?

relativism, roughly put, is the view that truth and falsity, right and wrong, standards of reasoning, and procedures of justification are products of differing conventions and frameworks of assessment and that their authority is confined to the context giving rise to them. more precisely, “relativism” covers views which maintain that—at a high level of abstraction—at least some class of things have the properties they have (e.g., beautiful, morally good, epistemically justified) not simpliciter, but only relative to a given framework of assessment (e.g., local cultural norms, individual standards), and correspondingly, that the truth of claims attributing these properties holds only once the relevant framework of assessment is specified or supplied. relativists characteristically insist, furthermore, that if something is only relatively so, then there can be no framework-independent vantage point from which the matter of whether the thing in question is so can be established.

relativism has been, in its various guises, both one of the most popular and most reviled philosophical doctrines of our time. defenders see it as a harbinger of tolerance and the only ethical and epistemic stance worthy of the open-minded and tolerant. detractors dismiss it for its alleged incoherence and uncritical intellectual permissiveness. debates about relativism permeate the whole spectrum of philosophical sub-disciplines. from ethics to epistemology, science to religion, political theory to ontology, theories of meaning and even logic, philosophy has felt the need to respond to this heady and seemingly subversive idea. discussions of relativism often also invoke considerations relevant to the very nature and methodology of philosophy and to the division between the so-called “analytic and continental” camps in philosophy. and yet, despite a long history of debate going back to plato and an increasingly large body of writing, it is still difficult to come to an agreed definition of what, at its core, relativism is, and what philosophical import it has. this entry attempts to provide a broad account of the many ways in which “relativism” has been defined, explained, defended and criticized.

explanation: