Explanation:
The observable visible spectrum of Cr(acac)3 complex is different from that of
[Cr(en)3]Br3 due to strength of bonded ligand in the coordination sphere.
en is a strong field ligand compared to acac thus pairing occurs. In both the complexes
Cr is in +3 state, configuration [Ar] 3d^3. There are 3 unpaired e in Cr(acac)3 whereas 1 unpaired e in [Cr(en)3]Br3 due to pairing.
The element with 4 protons in the nucleus in Beryllium.
mole=10 x 10⁻³ : 46 g/mol = 2.17 x 10⁻⁴
