STAAR Review - Con

How many valence electrons are in an atom of each element in Group 15 in the periodic table?

A student drew atomic models of four elements.

Based on these drawings, which element is the least reactive?

• Neon, because it has two energy levels with eight electrons in the second level

• Chlorine, because it has three energy levels with seven electrons in the third level

• Gallium, because it has four energy levels with three electrons in the fourth level

• Tin, because it has five energy levels with four electrons in the fifth level

Which chemical reaction involves the fewest oxygen atoms?

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As part of an investigation, students combined substances in a beaker to observe chemical reactions. They performed two procedures. They measured the mass of each substance before and after each reaction. The table shows their observations.

Assuming the students did not make any careless errors, what likely explains these changes in mass?

• Procedure 1: One of the products was a gas that escaped into the air. Procedure 2: A gas from the air reacted with one of the other reactants.

• Procedure 1: The reactants were liquids with different densities. Procedure 2: The reactants were combined into only one product.

• Procedure 1: One of the reactants was converted to thermal energy. Procedure 2: All the products were liquids.

• Procedure 1: All the reactants were liquids that evaporated. Procedure 2: A gas was formed as one product, and it escaped into the air.

Both the esophagus and the small intestine are involved in the digestion of food. The esophagus squeezes food into the stomach by wave-like muscle contractions. Peptidase enzymes in the small intestine break food molecules into smaller molecules. Which statement best describes changes to food during digestion?

• The muscle contractions result in physical changes, while the action of the peptidase results in chemical changes.

• The muscle contractions and the action of the peptidase both result only in physical changes.

• The muscle contractions result in chemical changes, while the action of the peptidase results in physical changes.

• The muscle contractions and the action of the peptidase both result only in chemical changes.

8.6C (2019-Q 16)

A large rock is motionless on a flat sidewalk. Which statement best explains why the rock remains motionless?

• F There are no forces acting on the rock.

• G The only force acting on the rock is directed toward the sidewalk.

• H The forces acting on the rock are all balanced.

• J The sidealk exerts an unbalanced force ont the rock.

(8.6A 2019-Q11)

The net force on a vehicle that is accelerating at a rate of 1.5m/s² is 1,800 newtons. What is the mass of the vehicle to the nerarst kilogram? (Hint: Force=Mass x Acceleration; F=ma)

(8.7B 2018-Q30)

• F

• G

• H

• J

Some students take care of a vegetable garden. When it is time to plant in the spring, the students leave part of the garden empty in order to observe ecological succession. Which of these will most likely occur first?

• Development of the topsoil

• Growth of weeds and grasses

• Growth of trees and shrubs

• Development of a stream

Based on the key, which type of tree is the sample from?

• Ginko

• Sweet gum

• Horse chestnut

• Honey locust