Which is the correct formula of calcium phosphide?

Step 1: Answer question 80. Sodium (Na) is known to be a very soft metal, easily cut with a knife.

• Answer: $\boxed{Na}$

Step 2: Answer question 81. Transition metal compounds are often coloured. Nickel (Ni) is a transition metal, and $\text{NiCl}_2$ is typically green. $\text{AlCl}_3$, $\text{BaCl}_2$, and $\text{KCl}$ are compounds of main group metals and are usually white or colourless.

• Answer: $\boxed{NiCl_2}$

Step 3: Answer question 82. Catalytic converters convert harmful gases like $\text{NO}$, $\text{NO}_2$, and $\text{CO}$ into less harmful substances. $\text{CO}_2$ is a product of complete combustion and is generally not further converted; it remains largely unaffected.

• Answer: $\boxed{CO_2}$

Step 4: Answer question 83. Organic compounds are primarily composed of carbon and hydrogen. Hydrogen is almost always present along with carbon in all organic compounds.

• Answer: $\boxed{Hydrogen}$

Step 5: Answer question 84. Magnesium (Mg) is commonly used to reduce alkyl halides, for example, in the formation of Grignard reagents ($\text{RMgX}$).

• Answer: $\boxed{Mg}$

Step 6: Answer question 85. A suspension is a heterogeneous mixture in which solid particles are large enough to be seen with the naked eye and will settle out over time. Colloids have particles that are smaller and do not settle, while true solutions have particles that are invisible.

• Answer: $\boxed{Suspension}$

Step 7: Answer question 86. Mixtures are commonly classified into three main types: solutions, colloids, and suspensions.

• Answer: $\boxed{3}$

Step 8: Answer question 87. The chemical symbol for the element sodium is $\text{Na}$.

• Answer: $\boxed{Na}$

Step 9: Answer question 88. The mass of a proton is approximately $1.672 \times 10^{-27}$ kg, and the mass of an electron is approximately $9.109 \times 10^{-31}$ kg. The ratio is: $\frac{1.672 \times 10^{-27} kg}{9.109 \times 10^{-31} kg} \approx 1836$ A proton is approximately 1836 times heavier than an electron.

• Answer: $\boxed{1836}$

Step 10: Answer question 89. The mass of an electron is approximately $9.109 \times 10^{-31}$ kg. None of the provided options are correct.

• Answer: $\boxed{None of the options are correct. The mass of an electron is approximately 9.109 \times 10^{-31} kg.}$

Step 11: Answer question 90. Calcium (Ca) forms a $\text{Ca}^{2+}$ ion. Phosphorus (P) forms a phosphide ion, $\text{P}^{3-}$. To balance the charges, three $\text{Ca}^{2+}$ ions ($3 \times +2 = +6$) combine with two $\text{P}^{3-}$ ions ($2 \times -3 = -6$). The correct formula is $\text{Ca}_3P_2$.

• Answer: $\boxed{Ca_3P_2}$

Step 12: Answer question 91. Table salt is chemically known as sodium chloride, which has the formula $\text{NaCl}$.

• Answer: $\boxed{NaCl}$

Step 13: Answer question 92. Copper(II) sulfate pentahydrate ($\text{CuSO}_4 \cdot 5H_2\text{O}$) is famously blue. Anhydrous copper sulfate is white.

• Answer: $\boxed{Blue}$

Step 14: