The question asks for the total number of elements currently recognized on the periodic table. This is a factual question related to general science, specifically chemistry. The periodic table is a fundamental tool in chemistry, organizing all known elements based on their atomic number, electron configuration, and recurring chemical properties.
Correct Option: B) 118 is the correct number of elements currently recognized on the periodic table by IUPAC.
The question asks about the number of naturally occurring elements on the periodic table. To answer this, we need to recall the classification of elements into naturally occurring and synthetic (man-made) categories.
A) 94 is the correct number of naturally occurring elements. This includes elements from hydrogen (atomic number 1) up to plutonium (atomic number 94), with some nuances for elements like technetium and promethium which are primarily synthetic but can exist in trace natural amounts, and neptunium and plutonium which are naturally occurring in trace amounts.
The question asks about the earliest attempts to classify elements. To answer this, we need to recall the historical development of element classification.
C) Metals and non-metals. The earliest and most basic way to classify elements was by distinguishing between metals (shiny, malleable, ductile, good conductors) and non-metals (dull, brittle, poor conductors). This distinction predates more complex chemical classifications.
The question asks about the term Johann Wolfgang Döbereiner used to describe the groups of three elements he identified. This refers to his early attempt at classifying elements based on their properties and atomic masses.
Correct Option: D) Triads — Döbereiner specifically named these groups of three elements "Triads" based on the Greek prefix "tri-" meaning three.
The question refers to Döbereiner's Triads, an early attempt to classify elements based on their atomic masses and chemical properties. Döbereiner observed a specific mathematical relationship between the atomic masses of the three elements in a triad.
Correct Option: B) Average. Döbereiner's Law of Triads states that when elements are arranged in increasing order of atomic masses in a triad, the atomic mass of the middle element is approximately the average of the atomic masses of the other two elements.
Which of the following are the Döbereiner triads?
a) Ca,Sr,Ba
b) Cl,Br,I
c) N,P,As
This question asks to identify Döbereiner triads from the given sets of elements. Döbereiner's triads were an early attempt to classify elements based on their properties and atomic masses. A triad consists of three elements with similar chemical properties, where the atomic mass of the middle element is approximately the average of the atomic masses of the other two elements.
A) Both a and b. As determined in the step-by-step analysis, both the set (Ca, Sr, Ba) and (Cl, Br, I) fit the criteria for Döbereiner's triads.