In this case a double displacement reaction will take place.
Empirical formula is the simplest ratio of whole numbers of components in a compound
molecular formula is the actual ratio of components in a compound .
the molecular formula for the compounds given are as follows
ethyne - C₂H₂
ethene - C₂H₄
ethane - C₂H₆
methane - CH₄
the actual ratios of the elements simplified ratio
C : H C : H
ethyne 2:2 1:1
ethene 2:4 1:2
ethane 2:6 1:3
methane 1:4 1:4
the only compound where the actual ratio is equal to the simplified ratio is methane
therefore in methane molecular formula CH₄ is the same as empirical formula CH₄
Answer : Half life and radioactive decay are inversely proportional to each other.
Explanation :
The mathematic relationship between the half-life and radioactive decay :
................(1)
where,
N = number of radioactive atoms at time, t
= number of radioactive atoms at the beginning when time is zero
e = Euler's constant = 2.17828
t = time
= decay rate
when
then the number of radioactive decay become half of the initial decay atom i.e
.
Now substituting these conditions in above equation (1), we get

By rearranging the terms, we get

Now taking natural log on both side,

By rearranging the terms, we get

This is the relationship between the half-life and radioactive decay.
Hence, from this we conclude that the Half life and radioactive decay are inversely proportional to each other. That means faster the decay, shorter the half-life.