Which of the following complexes will shows geometrical isomerism ?

When XO₂ is fused with an alkali metal hydroxide in presence of an oxidizing agent such as KNO₃ ; a dark green product is formed which disproportioates in acidic solution to afforda dark purple solution. X is :

For standardizing NaOH solution, which of the following is used as a primary standard ?

Which of the following compounds will most readily be dehydrated to give alkene under acidic condition ?