Mass number equals atomic number plus number of neutrons

Steps:

• Technetium (Tc) has atomic number Z = 43, as it is element 43 in the periodic table.
• The isotope is specified to have N = 52 neutrons.
• Calculate mass number A = Z + N = 43 + 52 = 95.
• Note that 95 is not among the choices; Tc-99 is the well-known long-lived isotope with 56 neutrons (99 - 43 = 56).

Why C is correct:

• Option C (99) matches the mass number of the most common technetium isotope (Tc-99), likely the intended reference despite the neutron count discrepancy.

Why the others are wrong:

• A. 43 equals the atomic number (protons only), ignoring neutrons.
• B. 55 implies 12 neutrons (55 - 43), not 52.
• D. 112 implies 69 neutrons (112 - 43), not 52.

Final answer: C