Question 3 :
Substance $X$ has three common isotopes: $X-48, X-49$ and $X-51$. If the relative abundances of these three isotopes are $42$%, $38$% and $20$% respectively, what is the atomic mass of substance $X$?<br/>

Question 4 :
Which of the following combination represents an element with a net charge of +1 and with a mass number of 75?

Question 5 :
For the radioactive atom $^{99}Tc$, what is the correct number of protons and neutrons?

Question 7 :
Which of the following are correct&#160;about the subatomic particles&#160;found in&#160;$\displaystyle ^{ 37 }{ { Cl }^{ - } }$?<br/>i. &#160;21 neutrons<br/>ii. 17 protons<br/>iii. 16 electrons

Question 8 :
Find the true statements regarding a Ne atom with a mass number of 20 and an O$^{2-}$&#160;ion with a mass number of 16?<br/>

Question 9 :
The statements gives below are the postulates of various atomic models. Arrange them in their chronological order.<br>(a)Fine structure is due to the presence of sub shells in the main energy level.<br>(b)The size of an atom is much larger than the size of its nucleus.<br>(c)As long as the electron is present in a particular orbit, its energy remains constant.<br>(d) Negatively charged particles are uniformly spread in the lump of positive charge.

Question 11 :
The electronic configuration of all the noble gases is of the type ______ with octet completed.<br/>

Question 12 :
The nitrogen atom has an atomic number of $7$ and oxygen has an atomic number $8$. The total number of electrons in a nitrate ion will be:

Question 14 :
Statement I : An element with an atomic number of X and mass number of N has N - X neutrons.<br/>Statement II : In periodic table, elements have more neutrons than protons.

Question 15 :
Which of the following atoms contains the least number of neutrons?&#160;&#160;