Why `Cu(OH)_2` is soluble in `NH_4OH` but not in NaOH solution ?

Ammonia forms the complex ion [Cu(NH_3)_4]^(2+) with copper ions in alkaline solutions but not in acidic solution. The reason for this is

0.80g is impure (NH_4)SO_4) was boiled with 100mL of 0.2N NaOH solution till all the NH_3 (g) evolved. The remaining solution was diluted to 250mL. 25mL of this solution was neutralized using 5mL of 0.2 NH_2 SO_4 solution. The percentage purity of the (NH_4)_2SO_4 sample is :

A 5.2 molal aqueous solution of methyl alcohol CH_3OH is supplied. What is the mole fraction of methyl alcohol in the solution ?

A metal complex having the molecular formula Cr(NH_3)_4Cl_2 ,Br have been isolated in two forms (A) and (B). The form (A) reacts with AgNO_3 giving white precipitate readily soluble in dilute NH_4OH while (B) gives a yellow precipitate soluble in concentrated NH_4OH . Answer the following questions : The formula of complex A is

FeSO_4 solution mixed with (NH_4)_2SO_4 solution in 1:1 molar ratio gives the test of Fe^(2+) ion but CuS04 solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu^(2+) ion. Explain why?

FeSO_4 solution mixed with (NH_4)_2SO_4 solution in 1:1 molar ratio gives the test of Fe^(2+) ion but CuSO_4 solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu^(2+) ion. Explain why ?

Ca(OH)_2 solution has pH greater than 7. Is it true or false?

Why is La(OH)_3 more basic than Lu(OH)_3 ?