In which of the following does the central atom exhibit an oxidation state of +2 ?
K2 [Ni(CN)4 ]
K3 [Fe(CN)6]
[Fe(C2O4)3 ]3-
[Cu(NH3)4 ]2+
K2(Ni(CN)4):
In this the anion will have a charge of -2 as 2K+ is present.
Then the charge on the central atom that is Ni can be calculated:
CN has a charge of -1, therefore Nickel x
x+4(-1) = -2
x = +2
[Cu(NH3)4 ]2+:
In this NH3 is neutral thus has a charge of 0 and the compound has an overall charge of +2.
Therefore the charge on the central atom that is Cu is +2.
Given below are two statements regarding conformations of n-butane. Choose the correct option. 
Consider a weak base \(B\) of \(pK_b = 5.699\). \(x\) mL of \(0.02\) M HCl and \(y\) mL of \(0.02\) M weak base \(B\) are mixed to make \(100\) mL of a buffer of pH \(=9\) at \(25^\circ\text{C}\). The values of \(x\) and \(y\) respectively are