The most stable complex among the following is:
Strong field ligand = stable complex.
[Pt(NH₃)₂Cl₂]
[Ag(NH₃)₂]Cl
[Pt(en)₂Cl₂]²⁺
K₄[Fe(CN)₆]
CN⁻ is a strong field ligand, forming a highly stable complex with Fe²⁺.
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