The question asks to identify the scientist who made the first attempt to classify elements into triads. We need to recall the historical development of the periodic table and the contributions of various scientists.
Correct Option: B) Johann Wolfgang Döbereiner (1829) — he grouped elements into 'triads' where the atomic weight of the middle element was approximately the arithmetic mean of the other two.
Johann Wolfgang Döbereiner, in 1829, observed that certain groups of three elements (triads) had similar chemical properties. He noted that in these triads, the atomic weight of the middle element was approximately the average of the atomic weights of the other two elements. For example, in the triad of lithium (Li), sodium (Na), and potassium (K), the atomic weight of Na (23) is approximately the average of Li (7) and K (39):
\[ \frac{7 + 39}{2} = \frac{46}{2} = 23 \]This was indeed the first significant attempt to classify elements based on their properties and atomic weights, preceding other major classification systems.
This question tests knowledge of early attempts at classifying elements, specifically Newlands' Law of Octaves. We need to recall the core principle of this law to identify the correct statement among the given options.
Correct Option: A) When elements are arranged in increasing order of atomic weights, every eighth element has properties similar to the first, like the eighth note in a musical octave.
The question asks for the correct statement of Mendeleev's Periodic Law as proposed in 1869. This requires recalling the fundamental principle upon which Mendeleev organized the elements.
Correct Option: B) The physical and chemical properties of elements are a PERIODIC FUNCTION of their ATOMIC WEIGHTS (atomic masses)
This statement accurately reflects Mendeleev's original Periodic Law. He used atomic weights as the fundamental property for arranging elements, leading to the periodic recurrence of properties.
The question asks for the most significant merit of Mendeleev's Periodic Table. We need to evaluate each option based on the historical context and contributions of Mendeleev.
Correct Option: A) He predicted the existence and properties of undiscovered elements (eka-boron, eka-aluminium, eka-silicon) which were later discovered (Sc, Ga, Ge respectively) with properties matching his predictions. This was a revolutionary aspect of his work, as it not only organized known elements but also guided future chemical research and discoveries, proving the predictive power of his periodic law.
The question asks to identify the pair of elements that Mendeleev placed in his periodic table in an order opposite to their atomic masses. This was a known anomaly in his periodic table, where he prioritized chemical properties over a strict increasing order of atomic mass to ensure elements with similar properties were grouped together.
B) Tellurium (Te, At.Wt.=127.6) placed before Iodine (I, At.Wt.=126.9) — Te has higher atomic mass but is placed before I. This is a well-known anomaly in Mendeleev's periodic table, where he prioritized chemical properties over the strict increasing order of atomic mass. Tellurium, despite having a higher atomic mass, was placed before Iodine to align it with elements of similar chemical properties.
The question asks about the unique characteristic of Group VIII in Mendeleev's original Periodic Table. To answer this, recall the structure and elements placed in different groups by Mendeleev.
D) Three triads of transition metals placed together: (Fe, Co, Ni), (Ru, Rh, Pd), and (Os, Ir, Pt). This accurately describes the unique composition of Group VIII in Mendeleev's Periodic Table.