Question 1 :
An element $A$ is tetravalent and another element $B$ is divalent. The formula of the compound formed by the combination of these elements is:

Question 2 :
An element $X$ combines with oxygen to form an oxide ${X}_{2}O$. This oxide is electrically conducting. Write the formula of the compound which is formed when $X$ reacts with chlorine.

Question 3 :
In sodium sulphide, the corresponding cation and anion attain the stable electronic configurations of _____ and _____ respectively.

Question 4 :
Calculate the molecular mass (u) of Sulphuric acid ($\displaystyle { H }_{ 2 }{ SO }_{ 4 }$).

Question 5 :
Total number of atoms represented by the compound $CuS{O}_{4}\cdot 5{H}_{2}O$ is:

Question 7 :
A cation M and an anion N have the following composition:<table class="wysiwyg-table"><tbody><tr><td>Element</td><td>Protons</td><td>Neutrons</td><td>Electrons</td><td>Mass no.</td></tr><tr><td>M</td><td>12</td><td>$\underline r$</td><td>$\underline p$</td><td>25</td></tr><tr><td>N</td><td>$\underline q$</td><td>17</td><td>14</td><td>$\underline s$</td></tr></tbody></table>M and N form a compound with formula $M_3N_2$. p, q, r and s are respectively ______.

Question 8 :
The charge on cation $M$ is $+2$ and anion $A$ is $-3$. The compound has the formula :

Question 9 :
An ion is produced as a result of gain or loss of electrons by an atom.&#160;&#160;In $Au^{3+}$ ion, 3 electrons are ___________by $Au$ atom.