letters are follows the pattern. the number-series $4,10,20,43,90$ should follow the pattern $\times2+1, \times2+2, \times2+3, \times2+4.$ so, $10$ is wrong and must be replaced by $(4\times2+1)$ i.e. $9.$ thus, the term $\text{j10r}$ does not fit in the given series. the correct term is $\text{j9r}$.
Hence, the answer is (A).