Question 1 :
Which of the following is the correct set of elements to Dobereiner's triads ?

Question 2 :
In Mendeleev's periodic table few elements that are chemically similar are placed in the same groups.<br/>

Question 4 :
Which periods were not divided into two series in the Mendeleev's periodic table?

Question 7 :
If the two members of a Dobereiner triad are phosphorus and antimony, the third member of this triad is&#160;:<br/>

Question 8 :
Mendeleev arranged the elements in increasing order of their atomic masses&#160;and according to their physical properties.<br/>

Question 9 :
Numbering of groups as 1, 2, ........... 18 was adopted by IUPAC in :

Question 10 :
Which of the following triads does not follow Dobereiner's law of triads?

Question 12 :
The elements whose atomic weight was corrected by Mendeleev are _______

Question 13 :
Assertion: According to Dobernier's, a group of three similar elements arranged in their increasing atomic weights so that atomic weight of middle is equal to the arithmetic mean of the other two elements. Reason: Atomic weight is equal to one twelfth of mass of a carbon atom.

Question 14 :
The first element of a group in many ways differs from the other heavier members of the group. This is due to:

Question 15 :
Who was the first to classify the elements into metals and non-metals?

Question 16 :
Dobereiner was the first person to illustrate the relationship between the ____________ of elements and their properties.

Question 17 :
Which of the following is the correct match?<br/>(a) Eka silicon - $\text{Ge}$<br/>(b) Eka aluminum - $\text{Ga}$<br/>(c) Eka manganese - $\text{Tc}$<br/>(d) Eka boron - $\text{Sc}$

Question 18 :
According to Mendeleev's periodic table, one element whose atomic mass is greater than that of nickel is placed before Nickel. Name the element:

Question 21 :
Assertion: According to Mendeleev, periodic properties of elements are periodic function of their atomic number. Reason: Atomic number is equal to the number of protons.

Question 22 :
In Mendeleev's periodic table, the gap was not left for one of the following elements. This element is:

Question 24 :
According to Lothar Meyer's curve, which of the following statement is/are correct?

Question 29 :
Assertion: According to Mendeleev, the properties of elements are a periodic function of their atomic weights. Reason: Mendeleev left the gap under aluminium and a gap under silicon, and called these elements Eka-Aluminium and Eka-Silicon.

Question 30 :
Most transition metals from multiple cations, that is, they have more than one possible amount of positive charge. Virtually all of the transition metals form dipositive $(2+)$ cations, along with one or more other forms. For example, titanium forms $Ti^{2+}$ ad $Ti^{4+}$, and cobalt forms $Co^{2+}$ and $Co^{3+}$.<br>The principal exceptions to this predominance of cations with a $2^{+}$ charge are scandium and yttrium, which form only tripositive cations. $Sc^{3+}$ and $Y^{3+}$, and copper and silver, which form cations with a single positive charge. $Cu^{+}$ and $Ag^{+}$.<br>[While copper also forms dipositive $Cu^{2+}$, silver exhibits the single positive state essentially exclusively.]<br>Which of the following offers a POSSIBLE explanation for the existence of $Cu^{+}$ and $Ag^{+}$?