3.50 moles of Ca = ? grams Ca

The mass of 3.5 moles of Ca is 140 g to two significant figures.

Explanation:

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.