What's the general formula for an alkane if n is the number of carbon atoms?

Option D  

Explanation:

Alkanes have nothing but carbon and hydrogen bonds, with no double or triple carbon bonds.  Each carbon in the chain will have a unit of CH2, with the other 2 carbon bonds connected to 2 neighboring carbons.  The terminal carbons will have 3 H's each.

So an alkane will have multiple (CH2) groups plus 2 CH3 groups on either end.  If there are n Carbons, there will be 2n Hydrogens plus 2 more for the end carbons.  

the answer is c i believe

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.