| \[_{\text{19}}^{\text{39}}\text{K, }_{\text{53}}^{\text{127}}\text{I,}\,\,_{\text{17}}^{\text{35}}\text{Cl,}\,\,_{\text{35}}^{\text{80}}\text{Br,}\,\,_{\text{18}}^{\text{40}}\text{Ar}\] |
| I. The correct order of increasing proton number is \[\text{KClBrIAr}\] |
| II. The correct order of increasing relative atomic mass is \[\text{ClKArBrI}\] |
| III. There is difference in the orders of proton number and relative atomic mass. |
| IV. The number of protons is equal to number of neutrons in all the given elements |
A) I and IV only
B) II and IV only
C) I and III only
D) II and III only
Correct Answer: D
Solution :
Atomic number = Number of protons Atomic number: \[\xrightarrow{\begin{matrix} \text{Cl} & \text{Ar} & \text{K} & \text{Br} & \text{l} \\ \text{17} & \text{18} & \text{19} & \text{35} & \text{53} \\ \end{matrix}}\] Increasing order of number of protons Atomic mass: \[\xrightarrow{\begin{matrix} \text{Cl} & \text{K} & \text{Ar} & \text{Br} & \text{l} \\ \text{35}\text{.5} & \text{39}\text{.10} & \text{39}\text{.95} & \text{79}\text{.90} & \text{126}\text{.90} \\ \end{matrix}}\] Increasing order of atomic mass The difference in the orders of proton number and relative atomic mass arises due to the presence of neutrons and number of protons is not equal to number of neutrons in all the given elements.
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