How many of these elements have lower electron affinity than fluorine?
$\mathrm{Cl}, \mathrm{S}, \mathrm{O}, \mathrm{N}, \mathrm{P}, \mathrm{Br}, \mathrm{I}, \mathrm{C}$

Atomic mass of $\mathrm{Cl}=35.5\mathrm{u}$ and that of $\mathrm{I}=127\mathrm{u}$. According to Dobereiner's triad rule, atomic mass of $\mathrm{Br}$ will be________$\mathrm{u}.$

Round off your answer to the nearest integer.

How many of the following are inner transition elements?

$\mathrm{Zr}, \mathrm{U}, \mathrm{Eu}, \mathrm{Au}, \mathrm{Co}, \mathrm{Os}, \mathrm{Ce}, \mathrm{Gd}, \mathrm{Hf}$

$\mathrm{M} \left(\mathrm{g}\right)\to {\mathrm{M}}^{+} \left(\mathrm{g}\right)+{\mathrm{e}}^{-}; \mathrm{\Delta H}=100 \mathrm{eV}$

$\mathrm{M} \left(\mathrm{g}\right)\to {\mathrm{M}}^{2+} \left(\mathrm{g}\right)+2{\mathrm{e}}^{-}; \mathrm{\Delta H}=350 \mathrm{eV}$

Which of the following is the correct statement with respect to the above reactions?