The periodic law, as we know it today, owes its development to two chemists.
(i) John Newlands (ii) Dmitri `I`. Menseleev
(iii) `J`.Lothar Meyer (iv) `J.W`. Dobereiner

The periodic law, as we know it today, owes its development to two chemists. (i) John Newlands (ii) Dmitri I . Mendeleev (iii) J .Lothar Meyer (iv) J.W . Dobereiner

When we use zener diode as a voltage regulator, its connection ……. (i) forward bias (ii) reverse bias (iii) should parallel with load (iv) should series with load

(i) Why do we classify elements ? (ii) What are the two criteria used in the development of Modern Periodic Table ? (iii) State the position of (a) metals, (b) non-metals and ( c) metalloids in the periodic table. (iv) Would you place two isotopes of chlorine, Cl-35 and Cl-37 in different slots of the periodic table because of their different atomic masses or in the same slot because their chemical properties are same ? Justify your answer.

(i) Newlands proposed the law of octaves. ii) The law of octaves was not valid for elements that had atomic masses higher than calcium. iii) Newlands left blanks for new elements in his periodic table. Which statement is wrong?

Ten students A, B, C, D, E, F, G, H, I and J Are sitting in a row facing west. (i)B and F are not sitting on either of the edges. (ii) G is sitting to the left of D and H is sitting to the right of J. (iii) There are four persons between E and A. (iv) I is to the right of B and F is to the left of D. (v) J is in between A and D and G is in between E and F (vi) There are two persons between H and C. Who are immediate neighbours of I ?

Mebdeleev's classification was a great improvement over contemporary tabulation of the elements by Newlands and Lothar Meyer because (i) it grouped the elements together more accurately in vertical columns. (ii) it left gaps for elements which were yet to be discovered in nature. (iii) it made possible the predication of the properties of elements that had not yet been discovered. (iv) it predicted that atomic masses of certain elements were incorrectely determined.

When Mendeleev developed his periodic table, chemists knew nothing about the internal structure of atom. His classification was based on their atomic wetghts. Several anomalies persisted in the table with regard to the correct order of atomic weights of (i) K adn Ar (ii) Co and Ni (iii) Te and I

Ten students A, B, C, D, E, F, G, H, I and J Are sitting in a row facing west. (i)B and F are not sitting on either of the edges. (ii) G is sitting to the left of D and H is sitting to the right of J. (iii) There are four persons between E and A. (iv) I is to the right of B and F is to the left of D. (v) J is in between A and D and G is in between E and F (vi) There are two persons between H and C. Who is sitting second left of D ?