Bacl2+k2so4=Baso4+2kcl why this reaction happens very fastly?

Q. A redox reaction among the following is
(i) $CdC{l}_2+2KOH\to Cd(OH{)}_2+2KCl$
(ii) $BaC{l}_2+K_{2}S{O}_4\to BaS{O}_4+2KCl$
(iii) $CaC{O}_2\to CaO+C{O}_2$
(iv) $2Ca+O_2\to 2CaO$.

Q. To 10 mL of 1 M $Ba{Cl}_2$ solution 5 mL of 0.5 M $K_{2}S{O}_4$ is added.$BaS{O}_4$ is precipitated out.What will happen?

Q.

Please answer this alone very fastly

This is from congruence of numbers

Find the last two digits of 3¹⁹⁹⁷

Q. $10$ mL of $1M$ $BaC{l}_2$ solution and $5$ mL of $0.5M$ $K_{2}S{O}_4$ are mixed together to precipitate out $BaS{O}_4$. The amount of $BaS{O}_4$ precipated will be :

Q. 5 g of $K_{2}S{O}_4$ were dissolved in 250 mL of solution. How many mL of this solution should be used so that 1.2 g of $BaS{O}_4$ may be precipitated from $BaC{l}_2$ solution ?