Maybe it is, maybe it isn't. We can't tell, until we see what "this" is.
Show us a drawing, an equation, an expression, a statement ... something !
I uploaded the answer t
o a file hosting. Here's link:
bit.
ly/3tZxaCQ
Answer:
The block's mass should be 
Explanation:
Given:
Cart with mass 
From the conservation of energy before mass is added,

Where
amplitude of spring mass system,
spring constant

Now new mass
is added to the system,


Here, given in question frequency is reduced to half so we can write,

Where
frequency of system before mass is added,
frequency of system after mass is added.




Therefore, the block's mass should be 
It is B: ionosphere. This has the ability to bounce radio signals