Mnemonic anchor: t-test and ANOVA are for means, chi-square is for counts. Decide which one your data are.
Here the result is a head count split into two boxes, malnourished or not, in two groups. That is categorical data summarised as proportions (30 percent rural, 20 percent urban). Comparing two proportions for significance is exactly what the chi-square test does, by checking how far the observed cell counts sit from the counts expected if there were no difference.
Knock out the rest: a paired t-test needs two measurements on the same individuals (before and after); ANOVA compares the means of three or more continuous groups; the standard error of the mean is a spread statistic, not a hypothesis test. None handles two proportions. So chi-square wins. Ref: Park PSM, 24e.