A mass of 135 g of a certain element is known to contain 30.1×1023 atoms....

A mass of 135 gram of certain element contain ${\displaystyle 30.1\times {10}^{23}}$ atoms.
The number of moles of certain element is given by,
${\displaystyle =\frac{30.1\times {10}^{23}}{6.022\times {10}^{23}}}$
${\displaystyle =5}$ The mass per mole (atomic mass) of certain is given by,
${\displaystyle =\frac{135}{5}}$
${\displaystyle =27}$
From periodic table we can conclude that element having 27 as atomic mass is aluminium
Hence
The element is aluminium