The compound A in the following reaction is :

The volume (in mL) of 0.1 N NaOH required to neutralise 10 mL of 0.1 N phosphinic acid is ___________.

An acidic solution of dichromate is electrolyzed for 8 minutes using 2A current. As per the following equation
Cr₂O₇^2- + 14H⁺ + 6e^– $$ \to $$ 2Cr³⁺ + 7H₂O
The amount of Cr³⁺ obtained was 0.104 g. The efficiency of the process(in%) is (Take : F = 96000 C, At. mass of chromium = 52) ______.

Let S be the set of all integer solutions, (x, y, z), of the system of equations
x – 2y + 5z = 0
–2x + 4y + z = 0
–7x + 14y + 9z = 0
such that 15 $$ \le $$ x² + y² + z² $$ \le $$ 150. Then, the number of elements in the set S is equal to ______ .