California CAST High School Science Practice

Practice physical, life and earth/space science with original CA NGSS-connected questions, evidence and engineering tasks.

This is independent, untimed practice using original classroom material and hypothetical data. It samples selected skills and curriculum connections; it does not cover every standard, assessment target or official item format. It is shorter than an official assessment and is not adaptive, calibrated, official released material, an official score estimate or evidence of full curriculum mastery.

18 original questions and tasks. Written responses have task-specific checklists and examples; they are not automatically scored. The material and data are fictional classroom examples.

This bank connects Grades 9–12 science. Official CAST is taken once in high school, in Grade 10, 11 or 12, as determined by your school. Engineering is integrated into the three science reporting domains.

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Request a hint when you need one. All levels use the same original questions.

Feedback reviewed for 0 of 18 questions in this selection. This is practice, with no official score.

Question 1 of 18 · Physical Sciences

Use conservation in reaction models · Curriculum connections: HS-PS1-7

Atoms and a sealed reactor

Original classroom material; people, sources and data are fictional.

Original classroom scenario with hypothetical quantities. A simplified model of water formation is 2 H₂ + O₂ → 2 H₂O. In a sealed reactor, 4 g of hydrogen and 32 g of oxygen react completely to form 36 g of water. No matter enters or leaves. The model is for reasoning about conservation, not instructions to carry out this reaction.

Which mathematical representation correctly supports atom and mass conservation in the reaction model?

Select one answer.There are four hydrogen atoms and two oxygen atoms on each side; 4 g + 32 g = 36 g.There are two hydrogen atoms before and four after; 4 g + 32 g = 32 g.Oxygen atoms disappear because the product is liquid.The number of molecules must stay the same in every reaction.

Official curriculum and preparation resources

Research reviewed October 1, 2026. Use the official practice platform for the state's item formats, tools and accessibility features. Local schools confirm testing dates, participation and individual supports.

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California CAST High School Science Practice

Atoms and a sealed reactor

Which mathematical representation correctly supports atom and mass conservation in the reaction model?

Official curriculum and preparation resources

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