Doubt from chemical kinetics

Question 3 and 7

Question 10 also

Isn't there is a mistake in K2 i think it should also raised to the power of -2 otherwise answer is coming which is not matching with answer key in question 4

Question 5 also i am not able to understand how to find Ea for second condition

Should i study radioactive disintegration chapter given in cengage or it's nor required for jee in chemistry?