Weathering and chemical substance weathering
<span>The
density of an object is defined to be its mass divided by the volume it
occupies. For this problem, the mass of the cube was given to be 25 g while its
volume is 125 cm</span>³. Thus, we simply divide 25 g by 125 cm³ to get the object’s density. We then calculate that the cube has a density of
0.2 g/ cm³.
A compass needle points north because the north pole of the magnet inside it is attracted to the south pole of Earth's built-in magnet . <u><em>And irons are heavily attracked to magnet</em></u> .So this is why iron needles used in compasses .
Answer: A. -396 kJ
Explanation:
The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states.
Reversing the reaction, changes the sign of 
On multiplying the reaction by 2, enthalpy gets multiplied by 2:
Thus the enthalpy change for the reaction is -396 kJ.
