S, T and U are the aqueous chlorides of the elements X, Y and Z respectively. X, Y and Z are in the same period of the periodic table. U gives a white precipitate with NaOH but this white precipitate dissolves as more NaOH is added. When NaOH is added to T, a white precipitate forms which does not dissolve when more base is added. S does not give precipitate with NaOH. Which of the following statements are correct ?
a. The three elements are metals
b. The electronegativity decreases from X to Y to Z.
c. X, Y and Z could be sodium, magnesium and aluminium respectively.
d. The first ionization increases from X to Y to Z.