For a good quality cement, the ratio of lime to the total of the oxides of $$\mathrm{Si}, \mathrm{Al}$$ and $\mathrm{Fe}$ should be as close as to :

Which halogen is known to cause the reaction given below :

$$2 \mathrm{Cu}^{2+}+4 \mathrm{X}^{-} \rightarrow \mathrm{Cu}_{2} \mathrm{X}_{2}(\mathrm{s})+\mathrm{X}_{2}$$

In chromyl chloride, the number of d-electrons present on chromium is same as in

(Given at no. of $$\mathrm{Ti}: 22, \mathrm{~V}: 23, \mathrm{Cr}: 24, \mathrm{Mn}: 25, \mathrm{Fe}: 26$$ )

Element not present in Nessler's reagent is :