Lead is often used to block out radiation
The answer is 3). This is because elements are the simplest form of a substance, and cannot be broken down any further. Compounds on the other hand are much more complex than elements and can be broken down INTO elements.
For example, Na, sodium, is an element and cannot be broken down further. H2O, water, is a compound and can be broken down into Hydrogen and Oxygen.
The SI base units for length is meter (m) and for time is seconds (s).
The given ratio is 

Converting mm/s to m/s as:
Since, 1 mm/s = 0.001 m/s
So, 
Since, zeroes to the left side of the non-zero number are not significant hence, the evaluation of
to three significant figures and answer in SI units is
.
Answer:
defined as a process in which mo heat transfer take place
Explanation:
is a process which occurs without transferring heat /mass between the system and it's surrounding.
The specific heat capacity of unknown substance is 1.333 g/j/°c
<u><em> calculation</em></u>
Specific heat capacity is calculated using Q= MCΔT formula
where;
Q(heat)= 800 j
M(mass) = 30 g
C(specific heat capacity) =?
ΔT( change in temperature) = 40°c - 20°c = 20°c
make C the subject of the formula by diving both side of the formula by MΔT
C is therefore = Q/MΔT
800j / 30 g x 20°c = 1.333 j/g/°c