Element!!! Points

Let r atomic number n and the molar mass be m [the latter can be eliminated without setting].

Then the molar mass of Hxroy is (X+M+16Y) and the molar mass of Hr is (1+M).

And because each takes 1mol, the difference in mass is 64g, therefore.

x+m+16y)-(1+m)=64, simplified to x+16y=65

Solve the positive integer solution of the equation, x=1,y=4 x=17,y=3 x=33,y=2 x=49,y=1

Obviously, only is true, so this hydrate is HRO4

If the r atomic number n is given, then the number of electrons outside the nucleus is also n, and the number of electrons outside the nucleus of 1mol r is n mol

In 1mol HRO4, the total number of electrons outside the nucleus of H and O is 1 1 + 4 8 = 33mol

Then 33-n=16, the solution n=17 is the answer (cl).

17,r is the element chlorine.

First of all, the gaseous hydride chemical formula Hr, where R is -1 valence, so its most ** is +7 valence, which is a halogen element.

1mol hxroy has 64 g more mass than 1mol h, and x=1,y=4 is judged to be x=1,y=4. (for halogen elements, and so it can be).

Then the number of electrons outside the nucleus is 1+8*4-16=17, that is, r is element 17 chlorine.

It's good to score chemistry questions in high school! The most important thing is skill!

1；Determine the range F Cl Bri i first

2；Hxroy is 64g more than 1mol HR mass; It's clear that there's only oxygen left after subtraction, and there's no way he's going to give you a disgusting number. This can be deduced that there is only one h! That is, hroy!

Wow! Isn't this y 4!

3；H, o Total number of electrons outside the nucleus 1 1 + 4 8 = 3333 - n = 16, n = 17, remember! It will be considered awesome, and the number of times specified is the real awesome!

That is, the answer skill must be mastered! Time is tight for chemistry exams! Calculations are best calculated at a glance.

Solution: 30 (3 5-1 2).

300 km.

A: A and B are 300 kilometers apart.

The distance between the two places is x kilometers.

3/5)x-(1/2)x=30

Solve the equation to get x=300

The midpoint is the 1 2 of the whole process.

The 3 5 of the whole course is more than the 1 2 of the whole course (3 5)-(1 2) = 1 10.

Therefore, the distance between A and B = 30 [(3 5)-(1 2)=30 (1 10)=300 km.

Xiao Ming's sail trembling stupid dynamic companion book is 4-1=3 times more than Xiao Hong's Donghuai.

Xiao Ming 120, Xiao Hong 30 copies.

Set Xiao Ming has a guess x book, and Xiaohong has a y book.

x=4yx-y=90

The solution is x=120

y=30 Xiao Ming has 120 copies of Xiao Hongsui and 30 anime books.

1.Set time x:70(x-4)-30x=200 x=12 Distance from home to school:

30x+70(x-40)=920(m) 2（1）.[5000+(5000+1000)] 2=5500(set) (2)

a+（a+1000）】/2=a+500 3.（51*80+49*90）/(51+49)=

minutes, walked 30 * 4 = 120 meters, in the same time, the distance run is 200 + 120 = 320 meters more than the distance walked, this same time: 320 (70-30) = 8 (minutes), so, Xiaohua walked for 12 minutes, ran for 8 minutes, so the distance from home to school is: 30 * 12 + 70 * 8 = 920 (meters).

2. (1) (5000 + 5000 + 1000) 2 = 5500 (sets) (2) (a + a + 1000) 2 = a + 500 (sets) 3, (80 * 51 + 90 * 49) (51 + 49) =

1. Set the walking time X, then run X-4

70(x-4)-30x=200

x=12 distance between the two places: 70 (x-4) + 30x = 9202 (1) the number of units in February: 5000 + 1000 = 6000 total in January and February: 5000 + 6000 = 11000 average: 11000 2 = 5500

2) The number of units produced in February: A+1000

The total number of units produced in January and February: A+A+1000

Average: (a+a+1000) 2=a+5003, total score of class A: 51*80=4080

Class B total score: 49*90=4410

Total: 4080 + 4410 = 8490

Average score: 8490 (51+49)=

1.Solution: It took x minutes to walk.

200+30x=70*(x -4)

The solution is x=12

Distance = 30 * 12 + 8 * 70 = 920

2.Solution: 5000+1000 2=5500

a+1000/2=a+500

3.Solution: (51*80+49*90) (49+51)=

1.Set up home to school x meters Walking time (x-200) 30 Running x 70 Because walking takes 4 minutes longer than running.

x-200）/30-4=x/70 x=5602 (1) [5000+(5000+1000)]/2=5500

2) [a+a+1000]/2

3.(51x80+49x90) (51+49)=min)).

If the distance between cities A and B is x kilometers, then the express train travels 2 9x kilometers per hour;

x=solution, x=360

Therefore, the distance between the two cities is 360 kilometers.

70*, at this time the slow train traveled the whole way (1-2 9*

168/（7/15）=360km

Let the two be separated by x kilometers.

then we get x = 150 km.

After a 30% increase in efficacy, then it takes: 5-30% hours.

Number of days originally planned: hours.

30% increase in efficacy 5 30% = days.

Originally planned to be completed in a few days = days.

After the efficacy is improved = days.

206-52) 2=77.

77 + 52 = 129 pcs.

So there are 77 rabbits and 129 chickens.

Chicken: x, rabbit: y, yes;

x-52=y

2x+4y=206

Solution: x=69, y=17

Solution: Let the water surface be raised by x centimeters. According to the title:

x=x=80

80 meters = 8000 centimeters.

So the water level rises by 8000 centimeters.

cubic meters = 3200000 cubic centimeters 32000000 (20 20) = 8000 centimeters.