When `CH_(3)CHO` is reacted in the presence of a base with excess of HCHO, which statement is true ?

The prducts of the reaction of HCHO and Ph CHO in the presence of concentrated base PhCHO in the presence of concentrated base are :

Excess of CH_(3)COOH is reacted with CH-=CH in presence of Hg^(2+) , the product is -

Excess of CH_(3)COOH is reacted with CH-=CH in presence of Hg^(2+) , the product is -

CH_(3)CH_(2)OH convert into CH_(3)CHO in the presence of

When CH_3CHO is treated with excess of HCHO in aqueous solution of Na_2 CO_3 , a product, used in making explosive, is obtained finally. Find the number of primary alcoholic groups present in one molecule of the product?