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

In a complexometric titration of metal ion with ligand
M(Metal ion) + L(Ligand) $$ \to $$ C(Complex) end point is estimated spectrophoto - metrically (through light absorption). If 'M' and 'C' do not absorb light and only 'L' absorbs, then the titration plot between absorbed light (A) versus volume of ligand 'L' (V) would look like :

Which of the following compounds will be suitable for Kjeldahl’s method for nitrogen estimation?

Sodium salt of an organic acid ‘X’ produces effervescence with conc. H₂SO₄. ‘X’ reacts with the acidified aqueous CaCl₂ solution to give a white precipitate which decolourises acidic solution of KMnO₄. ‘X’ is :