Answer is (4) - Pb.
According to the reactivity series of elements
- the elements which are above the hydrogen are more reactive than hydrogen.
- the elements which are below the hydrogen are less reactive than hydrogen.
Among the given choices, only Pb is placed above the hydrogen in the reactivity series and rest are below the hydrogen.
Hence, Pb is more active than hydrogen.
Answer:
watching a firefly is much different than watching a fire because watching a fire can make you hot and watching a firefly can make you happy
Answer: The final temperature will be 
Explanation:
To calculate the specific heat of substance during the reaction.
where,
q = heat absorbed =41840 J
c = specific heat = 
m = mass of water = 200 g
= final temperature =?
= initial temperature = 
Now put all the given values in the above formula, we get:
Thus the final temperature will be
make or become hot or warm is heating.
cooling is to become colder or cool down from a higher temp.
