Answer:
4. 1; 6; 2 — synthesis
Step-by-step explanation:
Decomposition reaction is defined as the reaction in which a single large substance breaks down into two or more smaller substances.
![AB\rightarrow A+B](https://img.qammunity.org/2021/formulas/chemistry/high-school/mqk8qn5xqc4ukvbj5yc8oev2c839dtqjkr.png)
Single displacement reaction is defined as the reaction in which more reactive element displaces a less reactive element from its chemical reaction.
The reactivity of metal is determined by a series known as reactivity series. The metals lying above in the series are more reactive than the metals which lie below in the series.
![A+BC\rightarrow AC+B](https://img.qammunity.org/2021/formulas/chemistry/middle-school/7osw1b4x4452t905agfspzd3qzv47dcdtr.png)
Synthesis reaction is defined as the reaction in which smaller substances combine in their elemental state to form a larger substance.
![A+B\rightarrow AB](https://img.qammunity.org/2021/formulas/chemistry/high-school/ijrjglvr18pbbvjgprr6ip0bbjamywa1l4.png)
The unbalanced combustion reaction is shown below as:-
On the left hand side,
There are 4 phosphorus atoms and 1 calcium atom
On the right hand side,
There are 2 phosphorus atoms and 3 calcium atoms
Thus,
Right side,
must be multiplied by 2 to balance phosphorus.
Left side,
is multiplied by 6 so to balance the whole reaction.
Thus, the balanced reaction is:-
Thus, answer:- 4. 1; 6; 2 — synthesis