Consider the following nuclear reactions
$${}_{92}^{238}M \to {}_Y^XN + 2{}_2^4He$$
$${}_Y^XN \to {}_B^AL + 2{\beta ^ + }$$
The number of neutrons in the element L is

The rate equation for the reaction 2A + B $$\to$$ C is found to be: rate k[A][B]. The correct statement in relation to this reaction is that the

The half – life of a radioisotope is four hours. If the initial mass of the isotope was 200 g, the mass remaining after 24 hours undecayed is

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