Question 2 :
Statement: In Dobernier classification of elements, the atomic weight of the middle element is equal to the average of the extreme elements of a triad.<br/><br/>State whether the given statement is true or false.

Question 3 :
The sum of the number of elements of fifth and sixth period is&#160;:

Question 4 :
In Mendeleev's periodic table few elements that are chemically similar are placed in the same groups.<br/>

Question 5 :
Which periods were not divided into two series in the Mendeleev's periodic table?

Question 6 :
The elements having more masses were placed before elements having lower masses in Mendleev's periodic table. Guess the pair of elements (higher mass, lower mass).

Question 7 :
If the two members of a Dobereiner's triad are chlorine and iodine, then the&#160;third member of this triad is&#160;:<br/>

Question 8 :
According to Mendeleev's periodic law, the&#160;properties of elements are a periodic function of:<br/>

Question 9 :
Two elements were elected by Mendeleev for studying the properties of compounds formed by other elements with the selected elements. What were the selected elements?

Question 11 :
The Russian chemist Dmitri Mendeleev is generally credited with organizing the chemical elements into a comprehensive periodic table in large part due to the fact that he was able to use his table to predict the existence of elements, like gallium, that were not known at the time $(1872)$, but were discovered later.<br>Which is the best explanation for why Mendeleev was unable to predict the existence of the noble gases (group $18$)?

Question 12 :
The elements which have taken the place of Eka aluminium&#160;is :<br/>

Question 13 :
Identify the factor that distinguishes each element from every other element in the periodic table ?

Question 14 :
Who was the first to classify the elements into metals and non-metals?

Question 17 :
Which of the following statements is not true about Dobereiner's law of triads?

Question 18 :
According to Lothar Meyer's curve, which of the following statement is/are correct?

Question 22 :
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 $Ag^{+}$?