The radionucleide $${}_{90}^{234}Th$$ undergoes two successive $$\beta$$ -decays followed by one $$\alpha$$-decay. The atomic number and the mass number respectively of the resulting radionucleide are

The half-life of a radioactive isotope is three hours. If the initial mass of the isotope were 256 g, the mass of it remaining undecayed after 18 hours would be

In respect of the equation k = Ae^-E_a/RT in chemical kinetics, which one of the following statements is correct?

The rate law for a reaction between the substances A and B is given by Rate = k[A]ⁿ [B]^m On doubling the concentration of A and halving the concentration of B, the ratio of the new rate to the earlier rate of the reaction will be as