In organic chemistry of alkanes, decane is the straight-chain hydrocarbon with formula C10H22. How many hydrogen atoms are present in one molecule of decane?

Introduction / Context:
Alkanes are saturated hydrocarbons that follow a general formula relating the number of carbon atoms to the number of hydrogen atoms. Being comfortable with this formula allows you to quickly determine the composition of many common hydrocarbons without memorising each formula separately. This question focuses on decane, a straight chain alkane with ten carbon atoms, and asks for the total number of hydrogen atoms in one molecule.

Given Data / Assumptions:

• Decane is an alkane with ten carbon atoms.
• Straight chain alkanes obey the general formula CnH2n+2.
• We assume decane is the normal (unbranched) alkane, often written as n-decane.
• The options provide different possible hydrogen counts: 22, 24, 11, and 33.

Concept / Approach:
For alkanes, which contain only single bonds between carbon atoms and are fully saturated with hydrogen, the general formula is CnH2n+2, where n is the number of carbon atoms. When n = 10, the formula becomes C10H(2*10+2) = C10H22. This means that in one molecule of decane, there are 10 carbon atoms and 22 hydrogen atoms. The question specifically asks for the hydrogen count, so we simply evaluate the formula and select the corresponding option.

Step-by-Step Solution:
Step 1: Recall the general alkane formula. For any alkane, the formula is CnH2n+2. Step 2: Substitute n = 10 for decane. Hydrogen count = 2 * 10 + 2 = 20 + 2. Step 3: Calculate the result. 20 + 2 = 22 hydrogen atoms. Step 4: Match 22 to the options provided; it corresponds to option 22.

Verification / Alternative check:
We can also think structurally. In a straight chain alkane, the two end carbon atoms each bond to three hydrogens (CH3 groups), and each internal carbon bonds to two hydrogens (CH2 groups). For decane, there are 2 terminal carbon atoms and 8 internal carbon atoms. So hydrogen atoms = (2 * 3) + (8 * 2) = 6 + 16 = 22. This structural check matches the general formula result and confirms that C10H22 is correct and that there are 22 hydrogen atoms in a molecule of decane.

Why Other Options Are Wrong:
Option B (24): This would correspond to C10H24, which does not satisfy the saturation rule for alkanes and is not a correct formula for decane. Option C (11): This is far too small; even pentane (five carbons) has 12 hydrogens, so decane must have many more than 11. Option D (33): This is too large for a saturated hydrocarbon with only 10 carbons; it would violate the general alkane formula.

Common Pitfalls:
Students sometimes misremember the alkane formula as CnH2n or mix it up with the alkene formula CnH2n. Another error is to count hydrogens incorrectly when drawing the structure, especially if they forget that internal carbons are CH2 groups and only the ends are CH3. To avoid these mistakes, always use the simple rule that alkanes are CnH2n+2 and double check by a quick structural count for important examples like decane.

Final Answer:
One molecule of decane contains 22 hydrogen atoms.