The mass number of titanium is:

47.78

The correct answer is option 4. 47.78.

The mass number of an element is the sum of the number of protons and neutrons in the nucleus of an atom of that element. Titanium (Ti) is an element with the atomic number 22, which means it has 22 protons in its nucleus. To find the mass number, you need to know the number of neutrons.

The mass number (\(A\)) is given by the equation:

\[ A = \text{Number of protons} + \text{Number of neutrons} \]

For titanium:

\[ A = 22 \text{ protons} + \text{Number of neutrons} \]

Now, to find the approximate mass number of titanium, you can refer to the atomic mass listed on the periodic table. The atomic mass of titanium is around 47.867 u (unified atomic mass units).

So, the mass number of titanium is approximately:

\[ A \approx 22 \text{ protons} + \text{Number of neutrons} \approx 47.867 \]

\[ \text{Number of neutrons} \approx 47.867 - 22 \approx 25.867 \]

The mass number of titanium is approximately 47.78, considering the significant figures in the atomic mass.