Tiến hành phản ứng nhiệt nhôm hỗn hợp X gồm 0,03 mol Cr₂O₃; 0,04 mol FeO và a mol Al. Sau một thời gian phản ứng, trộn đều, thu được hỗn hợp chất rắn Y. Chia Y thành hai phần bằng nhau. Phần một phản ứng vừa đủ với 400ml dung dịch NaOH 0,1M (loãng). Phần hai phản ứng với dung dịch HCl loãng, nóng (dư), thu được 1,12 lít H₂ (đktc). Giả sử trong phản ứng nhiệt nhôm, Cr₂O₃ chỉ bị khử thành Cr. Phần trăm khối lượng Cr₂O₃ chưa phản ứng là

A. 20,00%

B. 33,33%

C. 50,52%

D. 66,67%

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

Ever since humans inhabited the earth, they have made use of various forms of communication. Generally, this expression of thoughts and feelings has been in the form of oral speech. When there is a language barrier, communication is accomplished through sign language in which motions stand for letters, words, and ideas. Tourists, the deaf, and the mute have had to resort to this form of expression. Many of these symbols of whole words are very picturesque and exact and can be used internationally; spelling, however, cannot.

Body language transmits ideas or thoughts by certain actions, either intentionally or unintentionally. A wink can be a way of flirting or indicating that the party is only joking. A nod signifies approval, while shaking the head indicates a negative reaction.

Other forms of nonlinguistic language can be found in Braille (a system of raised dots read with the fingertips), signal flags, Morse code, and smoke signals. Road maps and picture signs also guide, warn, and instruct people.

While verbalization is the most common form of language, other Systems and techniques also express human thoughts and feelings.

(Source: TOEFL Reading)

The word "these" in paragraph1 refers to

A. tourists

B. the deaf and the mute 

C. thoughts and feelings 

D. sign language motions

Phản ứng viết không đúng là:

A. 4P + 5O₂ → 2P₂O₅

B. 2PH₃ + 4O₂ → P₂O₅ + 3H₂O

C. PCl₃ + 3H₂O → H₃PO₃ + 3HCl

D. P₂O₃ + 3H₂O → 2H₃PO₄