How many nuetrons are in selenium?

Answer 1

From wikipedia:"Selenium has six naturally occurring isotopes, five of which are stable: 74Se, 76Se, 77Se, 78Se, and 80Se. The last three also occur as fission products, along with 79Se which has a half-life of 295,000 years. The final naturally occurring isotope, 82Se, has a very long half-life (~1020 yr, decaying via double beta decay to 82Kr), which, for practical purposes, can be considered to be stable. Twenty-three other unstable isotopes have been characterized. "

74Se is stable with 40 neutrons

76Se is stable with 42 neutrons

77Se is stable with 43 neutrons

78Se is stable with 44 neutrons

80Se is stable with 46 neutrons

see the related link for a complete table on isotopes of selenium.

Answer 2

Selenium has multiple isotopes, but the most common isotope in nature is selenium-80, which has 45 neutrons.