Consider the following low-spin complexes $$K_3[Co(NO_2)_6],\; K_4[Fe(CN)_6],\; K_3[Fe(CN)_6],\; Cu_2[Fe(CN)_6] and Zn_2[Fe(CN)_6]$$ The sum of the spin-only magnetic moment values of
complexes having yellow colour is. _____ B.M. (answer in nearest integer)

We need to identify which complexes are yellow among the given low-spin complexes, then sum their spin-only magnetic moments.

The complexes are:

1. $$K_3[Co(NO_2)_6]$$: Co³⁺ (d⁶), low-spin → $$t_{2g}^6 e_g^0$$, 0 unpaired electrons, μ = 0 BM. Yellow in colour. ✓

2. $$K_4[Fe(CN)_6]$$: Fe²⁺ (d⁶), low-spin → $$t_{2g}^6 e_g^0$$, 0 unpaired electrons, μ = 0 BM. Yellow in colour. ✓

3. $$K_3[Fe(CN)_6]$$: Fe³⁺ (d⁵), low-spin → $$t_{2g}^5 e_g^0$$, 1 unpaired electron, μ = 1.73 BM. Red/orange colour, not yellow.

4. $$Cu_2[Fe(CN)_6]$$: Brown/reddish colour.

5. $$Zn_2[Fe(CN)_6]$$: White precipitate.

The yellow complexes are $$K_3[Co(NO_2)_6]$$ and $$K_4[Fe(CN)_6]$$, both with μ = 0 BM.

Sum of magnetic moments = 0 + 0 = 0 BM.

The answer is 0.