Question 3 : _________ is the smallest unit of matter which may or may not have an independent existence, but always takes part in a chemical reaction.

Question 6 : The symbolic representation of elements in a chemical compound is known as:

Question 9 : _____ are the basic units of matter and the defining structure of elements.

Question 11 : The ratio of radius of the nucleus to the radius of the atom is of the order:

Question 13 : Which of the following reactions is not according to the law of conservation of mass?

Question 17 : <p><span>16.8 g of metal carbonate on&#160;thermal decomposition gave 8 g of metallic oxide and 8.8 g of&#160;carbon dioxide. They follow:</span></p>

Question 18 : <p><span>A sealed tube&#160;containing phosphorus was weighed and heated carefully. After completion of the&#160;reaction, the tube was re-weighed under similar conditions. The weight of the&#160;tube will:</span></p>

Question 19 : A metal sulphate has the formula MSO$_4$. A chloride of the same metal will have the formula__________.

Question 21 : Which of the following statements is correct about the reaction given below?<span><br>$\displaystyle 4Fe\left ( s \right )+3O_{2}\left ( g \right )\rightarrow 2Fe_{2}O_{3}\left ( g \right )$<br></span>

Question 22 : Which of the following is a suitable example for illustrating the law of conservation of mass?<div>&#160;(Atomic mass of O = 16 g/mol, H = 1 g/mole)<br/></div>

Question 23 : Which of the following contains the greatest number of atoms ?

Question 24 : The number of gold atoms in 300 mg of a gold ring of 20-carat gold ($Au = 197$: pure gold is 24 carat) is:

Question 25 : <br/>The ratio of unpaired electrons present in d orbitals of $Co^{2+}$ and $Cr^{3+}$<span class="MathJax"><span class="MJX_Assistive_MathML">Co2+</span></span> is ____.