M(U) = 238 g/mol , M(F) = 19 g/mol

so

M(UF₄)

= M(U) + 4*M(F)

= 238 + 4 * 19

= 314.0 g/mol

2)

M(Mg) = 24 g/mol for Mg

it’s actually 24.3 but based on the question it seems like your meant to approximate it as 24 for simplicity??

then

from the formula

2 moles of Mg makes 1 mole of U

so n(Mg) = 2n(U)………………..(1)

also you have

m(Mg) = 24000g of Mg

which, using n = m/M , is equivalent to

n(Mg) = m(Mg) / M(Mg) = 24000 / 24 = 1000 mol of Mg

so, using (1), you make

n(U) = (1/2)*n(Mg) = (1/2) *1000 = 500 mol of U

which, using n = m/M again, is equivalent to

m(U) = n(U) * M(U) = 500 * 238 = 119000g = 119kg of U

all of the terms in brackets after n,m and M are meant to be subscripts eg m(U) means mass of uranium etc

M for molar mass, n for number of moles

Also

How do you write the subscript of 4 in UF₄ ?

I’d really like to know

.