In inorganic nomenclature, what is the common name for the compound with the molecular formula P4O10, often written using the empirical formula P2O5?

Introduction / Context:
This question is about the naming of a common phosphorus oxide in inorganic chemistry. The molecular formula P4O10 represents a phosphorus oxide that is widely used as a powerful dehydrating agent and drying agent in laboratories and industry. Historically and in most textbooks, this compound is referred to by the empirical formula P2O5 and called phosphorus pentoxide. Understanding this naming convention is important because many examination questions still use the older, common name even though modern nomenclature recognises the molecular formula P4O10 and the systematic name tetraphosphorus decoxide.

Given Data / Assumptions:
- The compound in question has the molecular formula P4O10.
- You are asked for the commonly used name in basic chemistry courses.
- Options include phospholipid, phosphoric acid, phosphorus pentoxide, and phosphorus decoxide.
- It is assumed you know the difference between oxides of phosphorus and phosphorus containing acids or biomolecules.

Concept / Approach:
P4O10 is a molecular oxide of phosphorus. When its composition is expressed in simplest whole number ratio, the empirical formula is P2O5, which suggests two phosphorus atoms to five oxygen atoms. From this empirical formula, the traditional name phosphorus pentoxide is derived. Although IUPAC nomenclature allows the systematic name tetraphosphorus decoxide for P4O10, the most common name encountered in school and competitive exam chemistry is phosphorus pentoxide. The other options, phospholipid and phosphoric acid, refer to completely different substances: phospholipids are biological molecules in cell membranes, and phosphoric acid is H3PO4, an oxyacid of phosphorus.

Step-by-Step Solution:
Step 1: Note that the given molecular formula P4O10 can be reduced to the empirical formula P2O5 by dividing both subscripts by 2. Step 2: Recognise that P2O5 corresponds to a pentoxide, meaning an oxide containing five oxygen atoms for every two phosphorus atoms. Step 3: Recall from standard textbooks that P4O10 is commonly referred to as phosphorus pentoxide, based on the P2O5 empirical formula. Step 4: Compare the options and eliminate phospholipid, which is a class of biological membrane molecules, and phosphoric acid, H3PO4, which is not an oxide. Step 5: Observe that phosphorus decoxide would be a more systematic description of P4O10, but it is not the commonly used name taught at school level. Step 6: Conclude that phosphorus pentoxide is the expected common name for the compound P4O10.

Verification / Alternative check:
If you consult inorganic chemistry textbooks or lab manuals, you will find P4O10 listed as phosphorus pentoxide, noted for its strong dehydrating properties and its reaction with water to give phosphoric acids. Chemical catalogues and reagent bottles also frequently label the substance as phosphorus pentoxide, sometimes adding the molecular formula P4O10 in parentheses. Systematic naming conventions acknowledge tetraphosphorus decoxide, but the overwhelmingly common term at the basic level remains phosphorus pentoxide. This confirms that option C is the correct choice in the context of general chemistry nomenclature.

Why Other Options Are Wrong:
Phospholipid refers to a major class of biological lipids containing phosphate groups and fatty acid chains and has nothing to do with a simple oxide like P4O10. Phosphoric acid, H3PO4, is produced when P4O10 reacts with water but is a different compound with hydrogen atoms in its formula. Phosphorus decoxide, while closer to a systematic description (decoxide suggests ten oxygens), is not the commonly used school level name and is not how this compound is usually referred to in exam questions. Therefore, these options do not match the expected common name for P4O10.

Common Pitfalls:
Students sometimes confuse oxides with the acids they form on hydration, leading them to pick phosphoric acid instead of the oxide itself. Others may be tempted by a systematically sounding name like phosphorus decoxide, not realising that exams rarely use that term. There can also be confusion between empirical and molecular formulas, with some learners thinking that P2O5 and P4O10 must refer to different substances. To avoid such pitfalls, remember that P4O10 and P2O5 represent the same compound, and phosphorus pentoxide is the widely accepted common name used in most basic chemistry contexts.

Final Answer:
The compound with molecular formula P4O10 is commonly called phosphorus pentoxide.