When the u-235 nucleus is struck with a neutron, the ce-144 and sr-90 nuclei are produced, along with some neutrons and beta particles. how many neutrons are emitted?

2 (2 neutrons are produced).

Explanation:

1) In the left side of the transmutation equationa appears:
²³⁵U + ¹n →

I am omitting the atomic number (subscript to the leff) because the question does not show them as it is focused on number of neutrons.

2) The right side of the transmutation equation has:

→ ¹⁴⁴Ce + ⁹⁰Sr + ?

3) The total mass number of the left side is 235 + 1 = 236

4) The total mass number of Ce and Sr on the right side is 144 + 90 = 234

5) Then, you are lacking 236 - 234 = 2 unit masses on the right side which are the 2 neutrons that are produced along with the Ce and Sr.

The complete final equation is:

²³⁵U + ¹n → ¹⁴⁴Ce + ⁹⁰Sr + 2 ¹n

Where you have the two neutrons produced.