Which of the following elements is alloyed with copper to form brass

Predict which of the following will be coloured in aqueous solution? $Ti ^{3+}, V ^{3+}, Cu ^{+},$ $Sc ^{3+}, Mn ^{2+}, Fe ^{3+}$ and $Co ^{2+} .$ Give reasons for each. 

Which of the following statements are correct?

$(A)$ The $M ^{3+} / M ^{2+}$ reduction potential for iron is greater than manganese

$(B)$ The higher oxidation states of first row $d$ block elements get stabilized by oxide ion.

$(C)$ Aqueous solution of $Cr ^{2+}$ can liberate hydrogen from dilute acid.

$(D)$ Magnetic moment of $V ^{2+}$ is observed between $4.4-5.2\,BM$

Choose the correct answer from the options given below:

Ammonia is a Lewis base. It forms complexes with cations. Which one of the following cations does not form complex with ammonia

Bessemer converter is used in the manufacture of

Although fluorine is more electronegative than oxygen, but the ability of oxygen to stabilize higher oxidation states exceeds that of fluorine. Why ?