Final answer:
The element you are describing is indium, which belongs to the same group as boron and has an atomic mass of approximately 115 u. It is a soft and malleable metal with the chemical symbol In.
Step-by-step explanation:
You are likely referring to the element indium, which is in the same group as boron (group 13 of the periodic table) and has an atomic mass of about 115 u (114.818 u, to be precise).
Indium has the chemical symbol In and atomic number 49. Despite being in the same group as boron, it exhibits different chemical properties due to its much heavier mass and position further down in the periodic table. Indium is known for its softness, malleability, and being fusible just above room temperature.
The atomic mass of an element is the weighted average mass of all its isotopes, as they naturally occur. For example, boron has an average atomic mass calculated by considering its two natural isotopes and their relative abundance. A similar process is used to determine the atomic mass of indium.