Final answer:
The element with 3 valence electrons, in the 4th row, and with an atomic mass more than Aluminum but less than Indium, is Gallium (Ga).
Step-by-step explanation:
The element described has 3 valence electrons, is in the 4th row (period) of the periodic table, and has an atomic mass less than Indium but more than Aluminum. According to the periodic table, elements in group 13 (III) are the ones with 3 valence electrons. Aluminum is in this group and is in the third period with atomic number 13.
The next element in this group in the fourth row is Gallium (Ga) with atomic number 31. The atomic mass of Gallium is approximately 69.7, which is more than that of Aluminum (approximately 26.98) and less than that of Indium (approximately 114.82). Hence, the element in question is Gallium (Ga).